I am either pregnant or going crazy, please help!!!?

Ok, I have 2 kids. One is 2.5 years and the other is 8 months old. I am still full time breast feeding my 8 month old. Also I am on the mini pill. I lost all the baby weight very fast, but with in the last 3 months I have been putting it back on. The weight feels like it is all in my stomach area. I have been exhausted, nauseated, having mood swings, etc. I thought to myself there is no way I could be pregnant again as I am on the pill and BF'ing but then I started to feel convinced that I am! I can't tell if I am just stressed from taking care of both kids, or if these are pregnancy symptoms. So, I have taken two tests and both are coming back negative. My stomach just does not feel right though. Any advice or experience you may have please!!