mate, you doing well, its just been 2 months, have some patience, you will get there....just keep up your motivation and eat well.

Progress is not fast on daily view, but if you compare 2 months ago and in 4 months ( 6 months total); you would be happy...so no worries...continue

I'm not a supplement guy (came out of it); so I emphasis on eating more. Dont worry about your body fat, at this point, you need them as you go heavier.

Again, nothing wrong in taking supplement; but remember as the name implies, its supplement and not replacement.

I do have back pain as well, do to active basketball in Uni; damn most of my knee and back injury came from there; and it gets worse as you age.

Hence I do physical back exercise to strengthen them together with lunges.

As for crunches; start slow; but if dislike them, no harm compensating with other core exercise. For me I just love them from school days.

My personal best (that I boast alot ...hahahha) is 60 situp in 60 sec.

Thats because DOMS normally happens on eccentric contraction and very much less on concentric contraction; when you overload.