If you don't feel strain on your muscles the following day after workout (please open question won't fit here)?

i don't know if you've ever heard of DOMS. but you get atrophied in your muscles after you initially start workin out so thats where the soreness comes from, but after some routine working out the soreness will subside. no soreness doesn't mean you're not working out hard enough.3 times a week is good. you can exercise your abs for days on end but not too much and not the same particular workout because you will get the plateau effect which means your body will be accustomed to the workout and the results will be minimal so mix it up a little! good luck to you.