I started on methotrexate in Jan of this year. My rhumey put me on folic acid when he prescribed methotrexate. I take folic acid everyday even when I take the methotrexate but only folic acid is in the morning and methotrexate is after my evening meal.
You don't say how high your mtx dose is. That said, folic acid is only one chemical bond from mtx and so is used up by the mtx. Thus, you should be taking it with your mtx. Depending on the dose, you may also need to take leucovorin calcium as a "rescue" from the mtx. It will stop the damage on healthy tissue which is a side line of chemo drugs. If you are at a low dose mtx, then you may not need the rescue, but the folic acid should be included. Ask your doctor to include a blood level run when you have your next visit.
As I told you before, the aches and soreness is caused by the dead inflammatory cells killed off by the mtx. Remember, inflammatory cells are rapidly dividing cells as are cancer cells. That is why the same drugs work for two different situations. Make sure you drink a lot of water and take it easy for the couple days post mtx. If you try and do too much, you can increase the stress on your body.
When I started on MTX 6 weeks ago I was also started on prescription folic acid immediately. I take the folic acid every day of the week except for the day that I take the MTX. I think different docs have different ways of prescribing the folic acid but it seems very important to have with the MTX.