My aunty had a fungus under a fingernail and it sounded like how you describe. It looked yellow and it also looked a bit gnarly (like rough tree bark) or misshapen. I don't remember how she ever fixed it.

My son dropped something really heavy right on the nail bed of his big toe years ago and it must have damaged the nail bed and it's always grown differently. It looks a little yellow and gnarly as well.

Just searched for fungus and toe nails and found a pic on a site. If it looks like that and you've had it all this time, I'd go see a podiatrist.

http://www.tiptopnails.co.za/115_art4_largeleft.php