If you want your periods to stop, the only way to do that is to take the contraceptive pill or another contraceptive (the combined pill gives the most control, but not everyone can take it, however quite a lot of people stop having periods altogether with the mini pill and other progesterone only methods). Your GP can also give you tablets that act as an anti-inflammatory and make your periods less heavy.
As for stuff over the counter, I usually take Nurofen Plus (ibuprofen with codeine), paracetamol and an antispasmodic (you can get Buscopan for periods cramps - it's not what I take but it's pretty similar). There are other things you can get over the counter - a pharmacist should be able to advise.