First i thought it was bed bugs so i bought the mattres cover cause i was itching everywhere and has rash all over my body but it went away. but i still itch in some spot of my body like my arms, wrist, butt, left inner thigh, lower back?

May be scabies: It could be another type of infestation like scabies or fleas. However, a mattress cover is not going to prevent bed bugs if you are infested with them. Other possibilities include an allergic reaction to a lotion, soap or laundry detergent.

Agree with Dr. F: If you have not seen the bugs, it would be prudent to see a dermatologist for a proper evaluation.