Asthma Forum - unrecognized bites ?

Every year, around this time when the weather begins to improve, I start finding itchy red lumps usually on my ankles or around my knees. To give you an idea of size they're usually similar size and appearance to a nasty spot or pimple.

They usually appear singularly or in pairs close to each other, and I nearly always discover (or start to feel them) in a morning after a night in bed.

When I was younger, I seem to remember that if I scratched them, they would worsen and even spread. I've seen nothing on the internet that suggests bites do this, and as I'm reluctant to scratch them now - don't really want to try it again to check!

My partner who shares the bed has never been effected and I have seen no evidence of bedbugs etc. Also, wouldn't they effect me all year round if they were present? We have no pets and rarely come into contact with animals, so I can't see fleas been the problem. I thought it could possibly be dust mites (we're generally very clean and tidy, but the bedroom does get cluttered regularly), but have since found out they don't actually bite.

It usually takes more than a week for them to start to disappear, and after they've gone, they leave a slightly darkened patch that seems to take months to actually fade away.

Various creams and gels ease the itching somewhat but don't really hasten the removal. If anyone has any ideas what might be causing these bites, I'd really appreciate some opinions. Thanks.