Med working, but side effects are awful. Looking for some support?

Hi! I'm on 25 mg of Methotrexate and my joint pain is actually pretty good right now! I've gone four weeks without a bad pain day (knocks aggressively on wood). However, I have a rheum appt this week and I'm really nervous about it. I've gotten sick a ton since she increased my medication dosage. I've had multiple yeast infections and sinus infections, and I've needed antibiotics several times. I need to see the doctor again because I'm currently dealing with a sore throat, hoarse voice, and swollen lymph nodes :( On top of that, my meds make me terribly nauseous. I've vomited several Methotrexate doses despite taking them on a full stomach after a big, healthy meal. I've tried taking a dose every 8 hours instead of every 12 like my rheum suggested, but it doesn't seem to make a difference.

She's mentioned switching me from pills to an injection to ease the nausea, but wouldn't the increased absorption cause further immune system issues? I don't even know what to do here lol. The med works so well, but it's also kicking my butt.

Update: Thanks everyone! I'm going to ask about the injections and maybe about increasing my folic because I really don't want to come off MTX. I neglected to share that I'm on 2mg folic (plus 1mg in my multivitamin). I can't take Dextromethorphan due to being on an SSRI antidepressant, though I've never heard that advice before and I'm intrigued! I'll be researching that later! :)

Update 1 month later: Holy moly! I feel worlds better on the injections. The flu feeling hits me hard, so I take my injection immediately before laying down to sleep. By the next morning, I feel just fine. Thanks everyone!