Had m/c in july&have been having sex now am having sore breast, cramps, weight gain.went for urine test&was negative but confused because of the symptom?

Hormones: If the pregnancy test was negative and yet you are having those symptoms of pregnancy, it's possible the symptoms are due to hormonal changes. Or it's possible you're weakly positive and it just hasn't shown up yet. If you've missed a period, take another test. If you haven't missed a period, wait until you do and then take a test. Good luck!