Need some advice!

Hello! My boyfriend and I are trying to get pregnant. We have been trying for two months now and nothing. I have never ever tracked my bbt or anything I'm relation to conceiving. I got pregnant at 17 and then again at 29. I was trying in 2011 when I got pregnant with my almost 2 year old ad it happened right away. I'm sort of frustrated that this third baby isn't happening so easily. I'll be 32 next month and I'm way more active than when I got pregnant the first two times. When's the best time to take the bbt? What's the best bbt thermometer to get and where to find a good one? Any help would be appreciated.