Possible Implantation Bleeding/ Other health factors complic

My fiance and I have been trying to get pregnant for about 4 months now. I was told at age 16 that it may be impossible for me to get pregnant and I have Polycystic ovaries. I also have a whole slew of other health problems including Diabetes, HPB, Hormone imbalance and High cholestorol. I started taking medications over a year ago and since then, I have been having regular periods. They were like clockwork every month until this cycle. I was supposed to start on the 28th of november and I didnt start spotting until Dec. 1st. I have not had regular flow at all and my spotting is very light ranging in color from brownish to pinkish. It was a little bit heavier yesterday than it had been, but as of today is is almost non existant. I am getting worried with all my health problem that it may be something other than pregnancy, But at the same time I am hoping that I am pregnant. I dont want to get excited about it tho for fear of the let down it could bring. Also how long should I wait before I take a HPT. I dont want to take one too soon in case of false reading! Thanks!