Such sudden onset bumps and itching is most likely to be due to an allergic reaction.
Insect bites are a possibility. Mosquite, horsefly, ticks, midge or gnats, fireants, chiggers, etc can cause such reactions. It could also be related to new medicines, foods, etc. Check out whether you started any new medication before the bumps started.. Also try to recall any new foods that you took, specially foods like nuts, some new types of meat, fish, etc before this occurrence. You could be having a food allergy. You should also watch out for any new soaps or detergents. Also try to recall any activities associated with this, like hiking to some place, cleaning the house or some area of the house, some hobby like wood working etc which coincide with the itching.
If you find anything which could have caused the allergy, then you have to avoid it. However, quite as often, no definite cause of such allergic reactions can be found, do not worry if this is so.
Meanwhile take Cap. Claritin (OTC) 1 cap. two times daily, this should cure the bumps and itching. Also apply 1% Hydrocortisone cream (available OTC) on the bumps
You should get relief from the bumps and it should heal within 2-3 days.
However, if the bumps persist or it gets worse, see your doctor.
Hope I have been able to clarify the situation for you and helped in resolving your query.
If you need more help, please let me know so l can continue to assist you.
Thank you and I wish you the best of health - stay safe!
Dr. P. Jyoti