May I know how long after (normal) delivery can we start exercising?

It depends on each individual for this as each woman has a different recovery rate. For me, although I only had 3 sitches, I had severe pelvic pains for at least 2 weeks and the pain only totally disappeared about 4 weeks post delivery. Only then did I started doing simple exercise like planks, stretching, etc. Remember not to take it too hard because although it may seem that you have recovered externally, internally your body is still healing. Try doing some yoga, it's pretty relaxing and helps tone your body too.