I took the plan b pill last tuesday. i'm now having really bad pains on the left side of my uterus. it's like normal cramps but on one side. is this a bad sign?

Possible: Without more information it is difficult to say if you should worry. First do a pregnancy test. If positive, see your GYN (or come see me, I am in Vegas). If your test is negative, then you should still see a doctor but it is less urgent than with a positive test. Cramps and bleeding is normal after plan B - but having them to one side could be a problem.