I just came back from the er with the same issue and the dr said I was about 4wks 5days and my hcg was low. It was 115. I have been told and also read that high hcg levels depending on what week does show a possibility of multiples, and 4300 seems pretty high to me. I just made an appt with my gyn. Goodluck to you!
The only way you can determine if you are having twins is by an ultrasound. I am 30 weeks with twins and my HCG levels weren't any different than a singleton pregnancy. If you think it's twins then you can schedule an appt with your OB to get an ultrasound.