Sore thighs after intercourse are caused by strained ligaments due to the long time spent in the same position during intercourse. If there is pelvic inflammatory disease, when having intercourse, the blood vessels in the pelvic cavity will dilate sharply and the uterus will contract, which will also implicate in causing thigh pain. If there is a lumbar disc herniation or lumbar muscle strain, coitus will compress the blood vessels of the lower limbs, which will also cause thigh pain. When this happens, you can observe it for 3-5 days, because the duration is not very long and it will not affect your health. However, if it is persistent, the presence of pathological factors will be considered at this time. You can go to the hospital and register with the pain department, have a CT scan to rule out lumbar damage, and choose oral medication for treatment according to the situation.