I had cramping and spotting on and off for 2 weeks between 6 and 8 weeks, it was very stressful as I expected the worst but I went on to have a baby. It should be checked though.
Sorry your doctor brushed you of thats not fair. Theres nothing much you can do, I just went on bed rest but I don't think it makes any difference.
Cramping is pretty normal in the beginning of pregnancy, and if you had only light spotting it could be implantation.
Best of luck, I hope you get to see a (kind) doctor soon.