The big itchy welts are due to a condition called hives. Hives are red, itchy welts or swellings on the skin that often come in clusters. They can appear anywhere on the body, cropping up either in one small area or covering large patches of skin. They most often occur as part of an allergic reaction. No one lesion lasts more than 24 hours, but new ones may continue to appear until the condition resolves.
The scab in the centre could be either due to your scratching or it could be that the lesions are due to scabies.
Scabies is a skin infestation by the itch mite. They burrow into the skin to produce intense itching, which tends to be worse at night.
Scabies produces small red bumps and blisters and affects specific areas of the body. The bumps (medically termed papules) may contain blood crusts.
Treatment is with permethrin (Elimite) creams that are applied from the neck down, left on overnight, then washed off. This application is usually repeated in seven days.
Wash linens and bedclothes in hot water and all those who were in close contact with you need to be treated too.
You can take anti-histamines such as diphenhydramine (Benadryl) or Cetrizine which help in providing relief from itching.
This will help even if it is an allergic reaction. you can also try Calamine lotion or Pramoxine gel/lotion on the affected areas to provide relief from the itching.
It's not hives or scabies. Would you like me to take a picture so you can see what it looks like?