Hi Jan
MTX can take 3-4 months to kick in and become effective. Likewise the side effects should start to settle down once your body gets used to the medication. Everyone's so different though so it's a bit hit and miss. Are you taking folic acid? This helps to counteract the side effects and should help with the nausea etc. You should have been prescribed it. I used to take folic acid everyday except MTX day.
One way to deal with nausea is to nibble on ginger biscuits which seem to work well. Alternatively split your dose into 3 x 2.5 doses, a.m., p.m. and evening. and take with a large glass of water. Try to remain active once you've taken them, it will help the meds to metabolize through your system more quickly. Also, avoiding rich foods, curries that type of thing can help.
If all else fails perhaps you could consider MTX by injection which goes straight into the blood stream thereby avoiding the stomach.
If you do a 'post search' you will find lots of info on side effects and MTX, it's often up for discussion
Lyn x