It is important to clarify that the effectiveness of an exercise does not lie in the number of repetitions but in its precision.
If your abdominals did not hurt it is because they were not doing any (or very little) exercise.
Abdonimal exercise can be done daily but as with any muscle group it should always be done within a routine (time and repetitions, ...
There's two separate issues here: definition and strength.
Definition is primarily diet.
Searching the web for ab/core exercises provides a wealth of options. Without equipment:
Crunch variations (heel taps, bicycle crunches, etc.)
Planks (and their variations, moving and static)
Flutter kicks (and leg lifts ...
Just body weight will do. Try this:
Lie down on your back. Legs straight
Make sure your back is neutral
While keeping your legs on the ground, curl yourself up (trying to bring your chest to your legs)
Do not use momentum to curl up. Curl up for say 10-15 degrees, pause, and then continue. This is done to remove the momentum due to the weight of your head
Training your abdominal muscles will surely help. After all our core connects our lower to upper limb. If it’s not efficient or “strong”, the kinetic chain is broken. I suggest to cut down on the weight to a level where you don’t feel that fatigue. If your core can’t take the load, somewhere else got to kick in to do it. We just don’t want that somewhere ...