Suggest Treatment For Fever, Gas And Constipation After Vaccination In Baby

My baby is 1 month & 15 days old. Yesterday he had vaccination. Now he has fever & is very discomfortable. He has also constipated & having lots of gas. Constantly he is in pain. Not taking milk. He is pressuring but not getting stool. What should I do. We have gently massaged his stomach in circular motion but....