Exercise and hemorrhoids

I'm 42 and I'm pretty fit. I cycle approx 70 miles a week and run at least once a week. I eat healthily too and am not constipated. Nor do I sit on the loo for long periods of time.

I went for a 5 mile run two weeks ago and in the shower afterwards felt really swollen and sensitive down below which turned out to be a hemorrhoid. This suddenly appeared from nothing.

I have had history of getting hemorrhoids over the past few years, but all relatively minor and they usually disappeared after a few weeks.

I tried proctosedyl cream for a week which helped reduce the pain but not the swelling. Two weeks later it still hasn't gone down despite having regular warm baths, using ice and trying apple cider vinegar (which made things worse!).

I'm a little confused about the advice. I thought exercise was a good thing as it gets the blood flowing, so why should a run cause the onset of hemorrhoids?

And secondly, should I stop exercising as this seems to have caused the problem? All the advice says to remain active and not sit around. So it's rather frustrating!

Any thoughts?