What Causes Blisters On Arm With Bumps On It?

i have a blister on my left elbow and got it around 4 days ago. it started off being a simple clear blister about 1/4 inch wide and it burned. im not sure how it formed it might have been the sun or it could have been scraped one too many times. it has been getting bigger since then and a couple days ago i was waking up and it would burn because the top layer of my skin was scraping back from my rough sleeping area. well today the skin has stopped expanding the blister because i have switched areas and the sheets of my bed had dry spots on them probably from the water that was around the blister. i put a new band-aid on and have been cleaning the blister for lack of a better term conservative amount of times. there was more water growing around it today and just about an hour ago i had consulted my friend who has completed a college cna course which she took about two years in. when i had showed her the blister with the bandaid off and the water broke through without me touching it. Though today i started to grow small itchy bumps on the same arm and one of my friends had the same thing happen to him about a week ago but he didnt have a blister just a lot of bumps on his arm and he has recovered since. What do you think i should do