there are a variety of GI tract medications which may be available from pharmacies , and iirc domperidone is one of those.
If you have an ongoing GI tract condition, the GP is likely to wish to prescribe appropraite medication and monitor you , referring onto to Gastro as appropriate - this would all be covered under your eligibility for the NHS.
What you have to remember is that as has been stated above , if you are eligible for NHS treatment and are taking a number of medications on a regualr basis , a PPC may be the most appropriate route