I saw that you aren't getting any luck or answers in general with this question so I did a bit of research for you (god bless Google).
-Here you have a lot of possibilities I'd suggest reading the site and see if you think anything would be helpful:
Link-Seven steps about it, can't hurt to read this too:
Link-And here you have reasons that might have caused it, how to treat it on your own without any drugs or doctors and if that doesn't help what to do, which doctors to visit, pretty much everything :
LinkI hope that some of this is helpful :)