Thanks for writing your query.
Muscular pains are common if a person is not accustomed to heavy exercise.
You should start by doing less exercises in initial days and then gradually increasing the exercise. This will help the muscles to get accustomed to the extra work and will not pain.
as described by you are common after abdominal crunches. You should stop exercising for few days to give rest to muscles and then gradually do the exercise as mentioned before. Always take opinion of your instructor about the duration and severity of the exercise.
If pain is severe you can take pain killer along with muscle relaxant
after discussing with your doctor.
Hot fomentation and application of pain relieving gel will give some relief.
I hope this is helpful to you.