I don't think it's a glitch. I've had weeks (in-game) pass without seeing a random dragon, and I've had times where I run into multiple dragons on the road out of Falkreath.
I thought you said you hadn't run into any dragons?... oh well
try finding a dragon cave, they like hiding them in the mountains but just start climbing random mountains and you will start seeing the dragon head symbol. go there and fight yourself a dragon. dragon appearance also increase after you take esbern up to the temple (either that or they decide they didn't like me for some other reason i have yet to determine)
also, if you run into a cave bear, just know the they are capable of facing a green dragon head to head on the ground, i got the dragon half health and this cave bear just came out and started tanking the thing! it was amazing when it B-slaped it to death (with a little help from my frost bow but it still did plent of damage itself!) it then came after me with still a little over half health!