First dose of Methotrexate

I had my first injection of methotrexate 10mg yesterday.Today I have a bad headache and feel really tired.I took 5mg folic acid tablet today as advised by the RA nurse and she told me I can take it every day apart from injection day if my side effects are bad.My question is how long do the side effects normally last and do they ever get better as your body gets used to the medication going forward.I am not on any other medication for my RA apart from a steroid jab I had a month ago.