losing weight after pregnancy

i gave birth to my son 4 weeks ago and i am breast feeding i gained 39pounds durning my pregnancy ( i am 5'10' and before i got prego my weight was 160) in the four weeks i have lost 20 pounds. i knew i was going to lose weight but i didn't think it would be this fast. i drink alot of water and i eat when i am hungry (which isnt that often) and i am not working out just normal house work.i just dont want to do anything to hurt myself or my child ?? so how fast is to fast?

i gave birth to my son about 13 months ago. i have lost 17 pounds since he was born. i tried to breastfeed but my son had trouble latching on. so after i went back to school i started to diet and exercise and it has been going great. i have lost almost 20 pounds in 2 1/2 months.