A little concerned about this bleeding :(?

i found out i was pregnant 2 weeks ago and 3 days later i started bleeing lightly, i went to the docs and they did a hcg test and an internal scan ( couldnt see anything not even a sac ) the nurse said my uterus was thick so i guess thats good? my hormone levels came back at 152, i went back 48 hours later hcg level 296.. then i went back again in 4 days or so and my hcg 520.. but i am still bleeding on and off.. sometmes i get cramps but they dont bother me, and the bleeding seems to be (up there and not coming down soz tmi) my pregnancy signs are still here but i would ike your oppinions since i had a miscarriage 2-3 months ago ( my first pregnancy ) what could this bleeding be? i have another appointment on friday for another scan but im upset just incase im gonna lose this baby :( the bleeding isnt getting worse but its always on my mind that its the start of a miscarriage, i had this fo 2 weeks or so now please help :(