That level is not low. Stop stressing. To give you an example I had a level of 21 which was considered positive at about 4 weeks - my doctor didn't even think it was low (just congratulated me) but I knew it was (from here) and I pushed for a second test which showed it had dropped to 11 (still positive) and then m/c a few days later at around 5 weeks. With this one I was over a thousand at about the same time so doc thought it might be twins, but is only a singleton. It just goes to show that docs often don't know what they are on about.

Oh, and don't stress about lack of symptoms. I've had very mild symptoms throughout this pregnancy and all is well.