I have diagnosed with nodular scabies I cannot get rid of it from my scalp (have had preexistis psoriasis in scalp) despite 4 rounds of oral ivermecti?

SCABIES SCALP. Scabies almost never affects the scalp! get a better diagnosis, preferably from a dermatologist. The chances are that what you have is psoriasis that is crusted over.
Oral plus topical. For encrusted scabies, you need to use oral Ivermectin along with topical permethrin. In addition, you must wash all of your clothes and bedding every day in hot water to kill the mites in the cloth. Scabies is tricky to treat sometimes but with time, a bit of care and patience it can be done, .