Prenancy, obesity and lack of periods.

Ok I've got a few questions to ask if that's ok. First of all I've not had a period since sept of last year, I've assumed this is due to me being so overweight (around 350 pounds) I've been sexually active over the last year with two different men and I've not used protection as I assumed without periods I would be unable to get pregnant. Although it's been just over a month since I had intercourse, I've started getting a brown discharge today. I've never had one before but when I put it into google almost every site I've read indicated that you get a brown discharge in early pregnancy. But is this even possible without periods? I've felt sick as soon as i woke up two out of the last three days (though this COULD be due to alcohol consumption) but I've not been sick, just been retching over the toilet, and after eating today i felt really sick for a moment and had to remain still until someone passed me a drink.

Any ideas what's going on?