Are you taking MTX injections or are you taking pill form?
With the pill form there tends to be more side effects like fatigue, nausea, flu-like symptoms not saying it can't happen with the injection but happens more often with the pill(it is also probably dependent of the dose amt.)
You will also need to take folic acid with your MTX as MTX is a folic antagonist, the doc should prescribe it with the MTX. Different docs px the folic acid different ways, my son takes 1mg ever day. Others take it every day but the day of the MTX and still others take it only on the day of MTX. Your doc should let you know how he wants you to take it.
You will take the MTX(pill form or injection) once a week. You will need your labs done quite often to make sure that all is well as MTX can affect your liver.
My son has been on pill form of MTX(25mg) since last year and he has had no side effects or problems with his labs. Recently, he started experiencing D the day of the MTX and the day after not every time but now and again.
Also, when you are out in the sun it will be good idea to wear a good sunscreen when on MTX.
Good luck hope all goes well!