Questions about ttc while breast feeding...

Ok, so I know it's possible to conceive while breast feeding, but how likely is it? My DD is 5 1/2 months and ebf. I don't want to stop breast feeding but we're ready start trying again. It's only been about two weeks, but I'm afraid it'll take longer than I'd like to conceive because I bf. Also, I don't get AF regularly because I bf. I've had it twice since she was born in April, but I think it's mostly because I changed the time of day/missed a pill. So how would I even know if I'm pregnant or not? Or when to make sure we dtd? Should I just start tracking my temp, get an opk?(I think that's what it's called) it only took 1 month to conceive DD so I'm not sure how to go about this or how often I should test because I feel I just won't know if and when I am. Any advise will help, thanks in advance!