I have a skin irritation or a rash on my back that is spreading. is there a cream or ointment i should use? the rash started on my upper back and spread to my lower back

This : This is very challenging to answer without a clinical examination so i would recommend you see a dermatologist. It could be many possibilities, including tinea versicolor (common on the back), eczema, psoriasis, dermatitis, folliculitis, fungal infection, or other possibilities. Read more about these conditions at the link below. I hope that helps a little!