16 and pregnant?

back in january, my dad had his wedding. he was getting married on a cruise, and i was going to be on my period that week. i was on birth control, so i skipped my sugar pills and started my next pack so i wouldn’t have a period. when i got back from the trip i stopped taking my birth control. a couple weeks later in late january/early february i ended up hooking up with my ex-boyfriend. it only happened once, we used a condom, and he didn’t even end up getting off.

in march i confided to my best friend that i hadn’t had my period since then. she gave me a pregnancy test [first response] to take, and it came out negative. the next month, when i still hadn’t started my period, i told my mom. she gave me a pregnancy test to take, but again it came out negative.

during may i had light spotting around when i’d normally start my period. but it only lasted for a day or two. then about a week later it happened again. and about another week after that it happened again. all in all, i spotted very lightly about three times in the month of may.

now it’s almost july and i still haven’t had a regular period. normally i’d start my period around the 7th or 8th. i haven’t really shown any symptoms of pregnancy other than gaining a lot of weight [since february i’ve gained about 20 to 30 pounds].

how likely could it be that i am pregnant? or is it more likely that there’s something else going on?