Everyone is different. It's not too low to worry about. >5 is positive for pregnancy.
That said, probably pretty early in your pregnancy. My first pregnancy (I m/c'd later at 8w5d) my Betas were 137 at 13DPO (so 3w6d) and 301 at 15 DPO (4w1d). This pregnancy, my Betas were 689.9 at 14DPO/IUI (4w exactly) and 1319.3 at 16DPO/IUI (4w2d). Even every pregnancy is different!