Sharp stabbing pain same spot-6 weeks pregnant

I'm 6 weeks pregnant and last night I was woken up by a sharp stabbing pain that was on the left side of my uterus radiating to my left hip. I had a FET of day 5 embryo late September. No the pain is on and off but in the same exact spot.... no bleeding (thank God).... what is this.... fertility clinic said if bleeding go to ER ..... they dont seem too worried...