Hello Chris and welcome to the site.
I would ask your GP regarding the infection. 5.61 is still a tad high.
Yes, apparently sex and cycling may have an effect on a PSA so it could have been that.
It could lso be an enlarged prostate but you really need to have the information from an expert to know for certain.
You are starting to think in terms of PC when it might be something else. Make an appointment with the GP. Rule out an infection (you may be "pleasantly" surprised to find that's what it is) and then ask to be referred to hospital. If there isn't an infection you need the 5.61 investigated anyway.
Lots of folk on here will offer advice and help. It's likely to get quiet over the Christmas period so I'm hoping that I have bumped you up the list before your post disappears.
Try not to worry too much. I know that if you hadn't gone ahead with the health screening you would probably be having a better Christmas than the one going through your mind, But look at it in a more positive light.
IF there is something there then the sooner it is dealt with the more successful treatment is.
Best Wishes
Sandra