Possible pregnacy? Maybe implantation bleeding?

Ok so here's the story. I have always had irregular periods. Usually i don't have them for months at a time or when i do have them they last for a long time. I hadn't had it for a couple months n i had sex once without protection on the 24th. It was a complete mistake because i have a boyfriend, so i took the morning after pill and started my period on the 30th, it was normal flow and ended on the 3rd or 4th of August. Then my boyfriend came back from Iraq on the 10th. We ended up having sex every day, anywhere from 2-3 times up until the 24th of August. we attempted to use a condom but every time it broke before he finished, so we ended up using the pull out method, although im not on birth control. Only one time did we use a condom when he finished and he noticed it has a little tear in it. Then on the 2nd of September, right before i went to bed i noticed a little spotting in my underwear, it was slightly brownish so i used a tampon. I woke up in the middle of the night and changed it, there wasn't hardly anything on it, but i used another one and when i woke up in the morning on the 3rd, there wasn't anything on it. Now it being the 14th my breast are really sore. The other nite i drank a glass ov MD and ate some hot cheetos and ended up throwing up. SMoking cigarettes makes me get a headache. Also i have been nauseated but no in the morning, mostly at night around the time i go to bed or when i take Benadryl, which i have to take daily because i have allergies. Could i possibly be pregnant? Or am i over reacting?