I had sex a few weeks ago now I have a bloody discharge with no odor. What's wrong ?

Several possibilitie. A bloody vaginal discharge can be due to a STD, a cervical polyp, taking a birth control pill late, cervicitis, or several other things. A full history, exam, and appropriate testing are necessary to know for sure what the cause is. Sorry I can't be of more help. See your PCP,GYN, or an urgent care clinic for a diagnosis and treatment. Best wishes.