hello and welcome. many years ago when i was an active workaholic i used to keep fit.
I say used to be as for three years have suffered a prolapsed disc through overworking my back.
I used to do the sit ups as being a woman didn,t want the sausage roll around my middle and liked a flat tummy.
I pulled muscles and wow was i in agony and seen my doctor and he said i had to rest for two weeks and prescribed anti inflammatories.
get it checked out and hopefully you be working out again before you know it.
good luck.