Skin eruptions causes redness after itching,usually after dinner, subsides in 30min,looks like multiple mosquito bites,frequent when constipative ?

Urticaria: This sounds like an allergic process- urticaria, where you can have hives after some stimulus. It's possibly triggered by something u eat or are exposed to. Sometimes no actual cause can be found -but it would be a very good idea to see an allergist who can help you. A good doctor might also question u to see EXACTLY what might be causing this. Keep a diary of symptoms to find a relationship.