I've had quite a few instances where I've been prescribed medication I shouldn't have been due to other medication, and the wrong medication/dosage and thankfully, me being on the ball, prevented an issue.
I take a document with me which has a list of medical conditions then a list of medication, set out in a clear way for medical people as to what is taken for what.
I also carry a copy of my repeat prescription with me. You can ask for a copy from your GP surgery, or, I find the pharmacy that deals with my repeat prescriptions tend to be sent spare ones every time so easy to get one there. Not all of my medication is on my repeat though as some comes via a special home care team and some only via a hospital pharmacy. I always keep the slips from those too.
Pharmacists are also useful for checking interactions. I've checked with them before now to make sure meds don't interact or for advice as to what should be taken when etc... They do tend to do medicine reviews periodically, where you can go to a private area, go through all your meds, make sure they are being taken properly, at the right times etc... So maybe worth asking for one?
Alternatively, ask a GP for a medicines review. They seem to have a system which flags up potential interactions with other medication you are on the system as being prescribed, as I know issues have been flagged and discussed with me for medications previously.