should i have a pain in my back when working on my abs it is almost like a strain pain but if i relax for 5 seconds it goes then i do a few more reps and it hurts

while im posting a new thread when i do pull ups it strains my abs like ive been working on them for hours but the feeling comes on about a day after

thanks

No, you shouldn't be getting the back pain you are. Is it your form thats causing the problem? Ask a trainer in
your gym for advice, if you have one?
If not come back and describe how and what you are doing for your abs and the problem may become evident.

Reaper  

It is likely your form. Sits up are terrible IMO, too much hip flexor involvement, plus straisn the lower back. Crunches are far better IMO.