So pleased you're feeling better @sherlockhomeless
PUBLIC SERVICE ANNOUNCEMENT:
Increasing pain, redness or swelling around a wound (even a tiny one like an insect bite) is a cause for concern. It doesn't matter what caused the wound, the protective layer of skin has been breached and infection can get in. It can even be infection that was just sitting on the surface of your own skin, not necessarily introduced by the biting thing.
Rapidly spreading redness, with or without 'tracking' means things are getting worse, A&E is needed. Also feeling or looking ill,shivery or feverish with it.
People at particular risk are those who are immunosuppressed (like OP), young babies, over 75's, people with diabetes and anyone who is pregnant or has recently given birth (diabetes and pregnancy both affect the immune system).
If in doubt, call 111. They have a very thorough assessment tool for wound/skin infection.