4w today - hcg77 - with spotting

Hey everyone just seeing if anyone has experienced this. I am 4 weeks today so really just found out. I have had 3 positive urine tests. Had blood work done I'm sitting beta hcg 77. Doctor needs to be go again on Monday (this must mean it's very low right now) today I started bleeding - well my cm was pink and now is darker. It has me all upset! Has anyone ever experienced this? I am also on prometrium since day 14.