What happens if you have sexual intercourse 3 weeks after cervical cryosurgery?

Probably nothing. The cervix heals very quickly and 3 weeks afterward cryosurgery things should be back to normal. Of course, infection is alwas a possibility....So always use protection!
Ok if healed. If the treated area has healed there should not be a problem. A post proceedure followup usually is done to evaluate the area.