need to express gas but cannot.

Hi,
Welcome to ehealthforum,
It is difficult to comment on the exact cause for the symptoms of rectal pressure feeling that you describe without examining you. The exact cause can only be made out after careful evaluation. Consider visiting your doctor/Gastroenterologist at the earliest for thorough examination and further evaluation to look for the underlying cause for the symptoms that you describe. Treatment options as appropriate (based on examination findings and investigations results) would be started/suggested to help you control the symptoms. Be in regular monitoring and follow-up with your treating doctor/Gastroenterologist and report any new/abnormal symptoms immediately. Drink plenty of water. Take adequate rest. Maintain healthy diet.
Take care.