What Is Causing Random Constant Bleeding?

I had my son in Nov 2009 where i capped out weight wise at 202lbs. Ive never been above 135lbs unless prego. Also my thyroid usually goes through the roof throughout pregnancy. At my sons 1yr check i also had my TSH levels checked and they were still too high at level of 7 and so doc continued me on 250mcg. I was taking Junel 1.5/30 birth control pills in the 21 day form and I also was taking my levothyroxine. By end of the summer, I lost a substantial amount of weight rapidly and so went in for TSH level check. I found out that I was at a level of -6. Bad! They only lowered my dose by 25 so Im taking 225mcg of levo. and I have a habit of missing a BCpill here and there and I would get confused on my days so I got switched over to Avian? Im not sure of name, it was only a partial fill. And since I now take Lessina 0.1mg/ 0.02mg 28 day. I have been pretty good about not missing any pills at all however 2 weeks after my last period, I missed 2 or 3 days in a row and began spotting so I just continued my pills. Then when it came to my week of sugar pills the 4th week, I just took another week of actual BC. I figured i would regulate myself out. I just got over my period early last week and have not missed any pills. Yet the last 3 days I have been bleeding randomly throughout the day usually towards the end of the day. I dont know if its just my new BC pills or my weight or just my body trying to straighten out. Ive always been a small person low weight and I just began taking BC after my son was born in 09, I used to always take the depo-shot. I havent taken a pregnancy test yet as i just had 2 periods in the last month. But what do you think is causing the random constant bleeding?