Cystitis from cycling??

[Ladylana]

Hi, I've recently started road cycling and am in training for a novice duathlon but I seem to develop cystitis after trips out on my road bike. No such problems on my mountain bike - so could it be the saddle?

I do wear padded cycling shorts but i think these may be a bit too big - could this be the problem?

Is this a common problem and does any one have any hints/tips??
Thank you :o