Heavy Bleeding but Rising HCG

I got a positive e pregnancy test on Monday and started bleeding Tuesday. It was light but got heavier with cramping. They tested my HCG on Tuesday and it was only 8. LMP 5.19.17 and approx 12-13 dpo now. The bleeding has stopped this morning and turned to light brown spotting. HCG is now 64 but bleeding is back and heavier with cramping. I still feel pregnant and the doc said that the numbers are increasing normally. They will likely redraw on Monday and scan in 10-12 days. Has anyone experienced this and still had a healthy baby? I'm certain I'm miscarrying. The doc says to be hopeful but only time will tell.