Any medfags here?

I got a bloodtest taken 4 days ago. Now all of a sudden I'm noticing large bruises on my underarm, but it's very yellow/bluish.

What the fuck happened and wat do?

They fucked up drawing blood. It's a bruising of the veins. Happens every time I donate blood. No big deal, do nothing it goes away in a week

It's normal, don't worry, the needle caused minor internal bleeding. It happens to me too with about 20% of syringe insertions. The yellowish colour is good, it means your body is breaking down the old blood. Don't worry OP.

That being said, I would advise taking a vitamin supplement, you may have a slight predisposition to bruising due to lack of several vitamins.