Anal itch symptoms and conditions

I'm a 32 year old male. This is probably the 5th time I've taken Zithromax. Unlike previous experiences, this time I got a horrible rash on my face, chest, neck, and little red spots all over my body. They itch horribly and I'm hoping they go away on their own. I am going on week two and they are still around. Last year, I was given a very strong antibiotic for an infection that just wouldn't go away. I took one dose and threw the rest out because the resulting full-body rash was horrible. I think that some of us may develop an allergy to certain families of antibiotics as we age. Either that or our immune systems are degraded. Who knows. I've also been dealing with chronic anal itch for 2 years now, and that is a horrible thing to live with. FEELING OLD!