Help! Why are half of my fingernails yellow?

I've never been the kind of girl to wear nail polish on my fingernails. I usually only wore a clear strengthening polish because I had naturally long squared fingernails and they basically looked like I had a natural french manicure, though a little weak (probably from lack of nutrients). However, I started wearing nail polish around September of 2009. The nail polish usually always chipped from the tips of my fingernails, sometimes even the very same day (especially after showering) I'd paint them because I didn't wear a top coat, and so I would either paint over the polish or remove it all completely and paint my fingernails again without really giving my fingernails a break. I also never wore a base coat underneath my fingernails during the entire time I wore nail polish. So about a month ago I decided to remove my polish completely, and I noticed my fingernails were a transparent yellow from top to bottom, but I wasn't too worried, I knew it was because I hadn't worn a base coat, so I used a freshly cut lemon to try to remove the yellowness... it didn't do much. Like I said, I wasn't too worried and I forgot all about the slight yellowness (it might have even faded away? I really don't remember...) but that's probably because soon afterward I kept painting my fingernails again for about a week or so, again no base coat or top coat applied. Again, the nail polish chipped on the tips of my fingernails first as usual (and from what was exposed of my fingernails under the nail polish looked normal, not stained) and this time I didn't bother to fix my chipped polish and left them like that up until 2 weeks ago. When I removed all the nail polish from my fingernails they looked pretty normal with some minimal green nail polish residue (since I had been wearing a dark green/jade color for the past few months) mostly on the bottom half of my nails and edges, but I was able to get them squeaky clean with polish remover, but a few days later I suddenly noticed my nails were bright transparent yellow, like a semi-arched strip across the fingernails just above the middle half of the fingernail up to the tips. Since I never wore a base coat while I wore my nail polish for so long, I figured that's what had stained my nails, plus people I had asked about it reassured me that's what had caused the yellowing, lack of oxygen and base coat, but that it would go away in a few days. Well, it's been more than a few days, it's been 2 weeks, it will be 3 this week, and I have not been wearing any nail polish since then, not even clear nor have I applied on any strengthening formula, and I have cut them really short (past my natural nail line) and I'm now waiting for them to grow until I can trim the last bit of the yellowness. But it's taking forever for them to grow. In the mean time, I've tried soaking them once in alcohol, as well as in a 50/50 warm water and hydrogen peroxide soak then scrubbing them with a new dish washing sponge (the two-sided kind, using the green rough part since I don't have a nail buffer or nail brush), as well as cleaning them with nail polish remover, and while the stains do seem to fade for a day or two maybe even 3, the yellowness doesn't seem to go away completely as it appears again. I'm really worried it may not be surface stains from nail polish and that it may be a fungus? However, it is no longer a bright yellow like it was the first day I noticed the yellowing, it is now a lighter yellow and only the bottom half of my nails are a healthy normal pink and all my nails haven't lost any luster, they're very smooth and don't have any white debris under them or any foul smell. Also, they are not painful to the touch, tingly or itchy or thick or have separated from the nail bed. They're not cracking, peeling or splitting, nor do they appear to be dry. Am I being paranoid about nothing? I've been telling myself that the yellowness is due to not wearing a base coat (lesson learned!) and the fact that the yellowness is on the upper half of my nails only means that the yellowness has been growing out, and it should be gone in a few more weeks/months, and I should just be patient, but I'm not so sure now. Because a) my thumb fingernails are hardly, if not at all stained with any yellowness compared to the rest of my 8 fingernails and b) some days I hardly even notice the yellowness on my fingernails and I get very happy and forget all about it, but sometimes when I wake up, I see that the yellowness looks darker than the day before. I can hardly sleep at night because it's all I can think about at night. I can't even enjoy watching t.v. anymore because when I look down at my fingernails I get upset. I'm afraid the longer I keep waiting for them to grow out, the worse they might become IF they're in fact infected with fungus and it'll be too late for any treatment. And, as the days go by, I can't really tell if the yellowing is growing out towards the tips or if it's growing in deeper into my nail bed