I'm having very severe pain in my stomach constantly since coming off of holiday with bad diarrhoea should i see a doctor or see if it goes away?

See below: Abdominal pain associated with diarrhea is often due to a viral gastroenteritis. However it's not possible to suggest that this is your problem without speaking with you. Imodium (loperamide) A.D. Is often prescribed to stop the diarrhea. If your symptoms are severe you should see a Physician.

Traveller's diarrhea: If the diarrhea is not severe and you are able to keep up with intake of fluid (I would recommend you take oral rehydration solution instead of water or juices) then you may wait for a couple of days and it may resolve on its own, but diarrhea following a recent travel may need evaluation for bacterial infection or parasitic infestation (you may need stool analysis)