Stomachache with rashes on body. Help!

I have been facing this issue which triggers due to many factors. Once in week or month, I generally get a stomach ache kind of burning sensation which lasts for max 39 mins and after that get terrible itching all over the body with rashes which lasts for an hour. I have took many medications to treat this problem but unable to find cause for the same. Generally, I observed I get this due to any consumption of spicy food or over eating during the day. However, sometimes inspite of controlling these factors, I get this pain and itching. It happens generally during night. The pain is terrible kind of feel like burning inside my stomach. I thought this might be acidity issues but I'm unable to find the cause for itching and rashes after the pain. Please help