Write to HMRC, NICO, EWC, Benton Park View, Newcastle NE98 1ZZ giving all details you can re addresses and employments in UK and ask for your National Insurance No.
Then download form CA 3638 and fill in and return for a forecast of your pension. If you are already Pension age you do not need to do this but contact The Pensions Service, International Pension Office , Tyneview Park, Whitley Road,Benton,Newcastle upon Tyne, NE98 1BA or Phone 00441912187777 0800 to 2000 mon. to fri.
Don't forget if you are getting an UK social welfare pension and Not getting an Irish social welfare payment then you are entitled to a medical card without means testing under EU rules.