Thrush - Ongoing issue, is it me?

Hi people,

I'm starting to get a little concerned and more importantly worrying about my partner!

Basically the last 3 sexual partners I've had have all developed thrush shortly after starting sexual intercourse with me. Most have had it before but it seems like when I'm in a committed relationship my partner tends to get it every couple of months or so.

Here is a bit of further info,

Partner is on the pill therefore we don't use condoms
I'm VERY clean and particular "down there". Always make sure he's cleaned properly in the shower!
No other health issues that I'm aware of
Always treat myself for Thrush when my partner has to stop any chance of re-infection
I'm tested for STD's regularly, always clear

As silly as it sounds when the past 3 sexual partners seem to suffer the same way and have never before it can't help make me feel like there's something dodgy about my sperm!! Silly I know but can anyone shed some light on the matter?

The doctor says it won't be me but I can't see how not and I hate seeing her uncomfortable.

Thanks in advance,
Concerned_2012