I've only had sex once. It was unprotected and with a close friend because I was manic (bipolar) and wanted to get the loss of my virginity over with with someone I trusted. They didn't ejaculate, just precum, but i later realized it was my peak fertility day. 

I had a lot of fatigue a few days after that as well as high sensitivity to smell and nausea and a few other symptoms. I wholeheartedly believed I was pregnant. When my period was a day or two later than normal (I have an irregular period but with a pattern of fluctuations. Normally a short one then a long one with fairly consistent lengths), I tested. Came back negative. Then my period came. It was much lighter than any for the past year before that, and much, much, much less painful. 

I decided I wasn't pregnant and basically forgot about it. 

The two periods after that went the same. Basically on time but way lighter and less crampy than is normal.

This month, I'm several days late, with none of the light cramping that usually precedes a period for up to three days before it starts. I've gone over stuff I'd ignored with an eye now looking at possible pregnancy. 

Could the past three periods have been breakthrough bleeding?

I've been having a lot of food cravings. (Rice for a while,potatoes right now, ice cream a while back, lots of other stuff.) I've gained twelve pounds in the past three months ish, four of which was in the past month, but I haven't eaten enough for it to be fat gain. I've been nauseous in the mornings, and if I didn't have such a strong stomach (i've vomited just over a dozen times in my life. It's so rare for me, I remember every time.) I probably would have vomited in the mornings. I'm sleeping a LOT, napping twice a day, and that's really odd for me. I'm retaining water. I'm a lot thirstier and have a lot more appetite. My waist 2" above my navel is 29", as it has been for about a year, but my waist 2" below my navel has gone from 34" to 38".

What are my chances, would you say? Am I just paranoid? (I'm not asking "am I pregnant" I'm asking "is it probably not, unlikely, possibly, or likely")