Talk to Pediatrician on Skin Allergy

My son has poxes on his right leg since a week. Got it checked from hospital. Doc said it seems like some kind of allergy and prescribed clomin anti allergy. Now the problem is that half teaspoon of clomin makes him sleep for at least 12 hours. Doc prescribed it thrice a day for 3 days. I don't feel like making my child sleep for whole three days. Is there any alternative to anti allergy syrup??? His current weight is 12 kgs. Pics are attached for your reference.