The bumps on your neck and arms being very itchy suggests it may be cholinergic urticaria
and high dose long acting antihistamines will help.
, joint pains
, rash that does not disappears but looks like a bruise
or leaves a scar needs further investigating to ensure that it is not a form of vasculitis
(inflammation of blod vessels). However, just a fever is not suggestive of this condition, and a viral infection triggering the ithcy rash is usually the most likely explanation.
If the fever continues, do ensure an infection screen is done and you are on the right antimicrobials but continue on the antihistamines until the rash is well gone for 2 weeks and then stop the antihistamine tablets.