I had my last period on October 29th? I think. I'm a couple days away from being 18.we used condoms but once or twice we were unprotected. I'm wondering if it could be from my mom being 2 to 3 months pergnant if that could be throwing me off my cycle. I'm bloated having pains in my low stomach area. And really sore breast and nipples. Been consitpated for a little then its kind of going away, I'm really nervous and don't really know what to do. Please help my or give me advice. I'm not really having signs of pregnancy but its like a mixture of pregnancy and period signs. I've taken 4 pregnancy test and they've all been negative. Please help!!

Impossible to know here. You could be pregnant - a few women test negative for longer than most. Test using first morning urine.
You could be having a phantom pregnancy, which will have virtually all the signs of a real one, including getting larger.
You could have just skipped a period and are having hormone fluctuations, not uncommon at your age.
STOP having unprotected sex! For all you know you are worrying yourself into these symptoms.
Keep testing.

Stress is a major factor of making your period even later, just try to relax and if your still worrying in a couple of days visit your doctor who will perform a blood test. My advice if you are not trying to conceive would be to also speak to them about birth control as hoping you won't get caught is not an effective form of contraception.