My dog is farting all the time lately---why!?!?

I've been reading the articles online that other people have asked this same question, and almost all answers say it's the diet...but I don't get it because she's been on the same diet for a few months now and I've never even noticed this farting thing once, now it's like constant! It smells SO bad. I blamed my boyfriend the first time, but I believed him this time when he said it was the dog cause it was just the deadliest nasty smell ever! Any ideas as to why this may be happening? She's a puppy, 8 months, black lab...we just started spending tons of time outside since winter is over and the snow is gone...might that have anything to do with it? IDK but it's got to stop!!!!