What has caused this bruise?

[SecondClassReturnToDottinghamPlease]

Last Thursday I found a lump on my arm. It was about the size of a pea. No obvious reason why, no broken skin to indicate it was a bite, it didn't hurt. The skin around the lump started to bruise. 5 days later the lump has gone down significantly but is still slightly raised and still hard. The bruise has continued to spread and is now a couple of inches across and you can clearly see the lump in the centre. Any clues?

Have you sat with your arms on a table (dinner table/ picnic bench) ? Could you have just leant on a small lump of wood on a table or briefly grazed/knocked into a prominent cutlery handle or something? It looks like the under bit of your arm that would rest on a table.

It's possible I suppose. But it doesn't hurt, I would have thought it would hurt if I had knocked it?

I had something like that on my ankle a while ago. Hadn't knocked it, nothing. It went eventually.

Possibly poor circulation. Blood not flowing as it should?

Strange isn't it @Charlingspont !

It could be poor circulation, but why would that cause a lump?

I've had insect bites that have done that.

Insect bite was my first thought, but there is no puncture wound and it's not itchy at all.