How can i tell my gyn about bleeding after masturbation without it being super awkward? also what is he likely to do? should i expect a pelvic exam?

No reason to be shy: There is no reason to be embarrassed about this. There is nothing that you could say to an Obgyn that we have not heard before. Masturbation is a universal human behavior so this is not going to be a surprise to your doctor. They will likely do an exam to make sure nothing is wrong and then discuss options for menstrual cycle regulation.