Had an hcg level drawn 2 days before my period was to start and it was at 19. Had another blood draw today 1 day after missed period and it is at 108. The Dr wants to do another blood draw in 3 days. Do I need to be worried about something?

Not to worry . You have normal or abnormal pregnancy in your body. And the only way to monitor it at this low level of bHcg is to keep repeating it eVery few days..in normal pregnancy it doubles about 48 h. In abnormal it grows slower or drops. Sono is useless in early pregnancy. Have patience .
No. You are definitely pregnant and your HCG is doubling as it should. The doctor is just being cautious as you would want. There may be other things in your history that make this caution more important. Best wishes to you and the baby.