HCG not doubling

This is my first pregnancy and just found out on Friday! I have pcos and have been on letrozole the past 5 months and I only ovulated 3 times. This last round I tested on Monday and got a BFN and then went to the infertility specialist that day and he said to test again before the next round of letrozole. So I tested again on Friday and it was a BFP! I got my HCG checked on Friday and it was 54 and they wanted me to check again today and it was 88. I'm so worried, they told me because it didnt double they want me to check it again on Wednesday. I feel fine, no pain, no bleeding. I'm worried I'm going to have an ectopic pregnancy. Has anyone had anything like this and there pregnancy was normal?