hrmmmmm it is possible to strain any muscle in your body, but what you're experiencing could be the very normal "after workout" pain you get in muscles when you've exercised them properly... i suppose you know that any proper weight bearing exercise tears the muscle fibres and the muscle rebuilds while you rest and this is what actually makes them bigger and stronger? could be that... in which case, it's good, you're working out properly!!!! abs don't need as many rest days as other muscle groups but take at least one inbetween working them out. if you feel you are especially weak right now, take 2, or even 3 rest days.
i can recall times when i have been unable to laugh/cough without pain in my abs after a good workout... funny, next time i did my situps, i did them better!

but if it's really crippling, inhibiting pain, then it could be an injury... in which case a physiotherapist might be on the cards...