I got an adverse reaction to advil. Rash all over. Looks like urticaria. I took one 10 mg claritin (loratadine). Can I take another soon after? Painful itchy hives

Yes. If the hives are itchy, you may up the dose of Claritin (loratadine) to 4 x daily but this may cause some drowsiness. Allegra is another option. If the problem gets worse, you will need to see your doctor. Consult an allergist to find out whether you are "sensitive" to all NSAIDs or only to Advil.
Treatment for hives. The most effective antihistamine to treat hives (urticaria) is diphenhydramine (Benadryl), available over the counter, although this can make you sleepy, so avoid alcohol and do not drive. 25 or 50 mg by mouth every 6 to 8 hours. If any facial or tongue or throat swelling or hoarseness of you voice develops, seek immediate medical attention.