No period, but i bled when i had sex??

okay i need help.
i have an irregular period.
but lately since christmas it has been near the end of the month. cus i always have it on christmas :cry:
my mom says your period seems to flow around the same time as the ppl ur mostly around
and i'm only around my father my brother my boyfriend and my friend but who are all guys.
the only woman i'm around is my mom but she no longer has a period due to surgery and i only see her about once a week.
now today is the 10th and i should have had my period lets say 10 days ago maybe a few more.
when i was supposed to have my period last month my boobs got sore. my back hurt a little for like 2 days. i had pretty bad cramps.
but i only spotted when i would make a bowel movement. like 3 times maybe 4.
now my boobs have stopped hurting as bad but they are still sore. almost 3 weeks of sore boobs, sucks
and i usually dont poop but a few times a week
however now i seem to everyday and i have lil cramps every day but only when i have to poop.
then on the 7th i had sex with my boyfriend and there was a lot of blood. it looked like i was on my period having sex from the amount of blood. but that was the only sight of blood since i was spotting. and i know he wasn't to big or to rough lol

am i maybe pregnant, or got a disease or have something wrong with me?

one more thing, i used to eat once a day. everyday. just cus that's what made my stomach feel good. eating makes my stomach hurt and when i started weighing 96 lbs. i decided to eat more to be healthy. could this change in eating be the cause.

idk just rly hope i'm not pregnant. i'm 18, no job, no money. live with my dad. and i'd def have to leave before he found out, somehow. but plz reply