Go and see your GP. It's always best to get professional medical help than advice from strangers on the internet, particularly .as you have a medical condition.
However (because I know people will probably mention this) you can use an online TDEE calculator to work out how many calories to be eating to gain, maintain or lose weight. Make sure that you also eat balanced meals with the right range of foods to get the required nutrition like protein, carbs, minerals and vitamins etc. Skipping meals won't help and will give you other health issues!