They could be spider bites or from other bugs. I swear I am not trying to scare you but I want to tell you what happened to me. A couple of years ago I kept waking up in the morning with big welts on my legs and for the life of me couldnít figure out what it was. Well after a couple of weeks I went to wash all of my bedding and I had one of those cotton pads on top of my mattress and when I pulled it off there was a scorpion. That ****** had been biting me for weeks. If I were smart I would have investigated all of my bedding right away but I guess I wasnít thinking at the time. Anyways, first thing is to remove all your bedding and wash it just in case and pull your bed out a little and clean around and under it just to be safe. If you do find a scorpion be careful because they travel in pairs and three weeks later his mate found me in the bed again.
My mosquito bites also turn into bruises after a couple of days so that is a possibility also. If you go outside and notice them you should put some of that spray on you that keeps mosquitoes away. Ever since I moved to Texas this is a must. Itís funny because when I lived in Arizona and got bit they never were a big deal or left bruises.
Also, (sorry, I swear I didnít mean to write a book) a spider bit my mom about 4 years ago and that spot on her leg turned black. She didnít realize it was a spider at the time but after about a week of it getting worse she went to the doctors. The doctor gave her medication and said if she hadnít gone in sooner they would have had to amputate her leg. They think it was a brown recluse. She is fine now but that spot is still black and gross. If your bites look really bad and donít seem to get better soon you should probably go to the doctor. Again, sorry so long.