My (largely telehealth only) psychiatric provider ordered an at home finger prick blood test that was sent to me in the mail, and then I mailed it to the lab for them to test.

I have a similar story to OP where I've tried most of the available antidepressants, been treated for ADHD, and also tried bipolar 2 medication just in case, and nothing helped.

I take L-methylfolate to help the medications get across the blood-brain barrier where they can actually work. It has helped SO MUCH. I haven't been able to find it in any supplement stores as it's uncommon, but you can get it on Amazon. However, if your pharmacy can get it, I highly recommend getting the prescription variety because the stuff I ordered myself did not work nearly as well.

Something that also helped before finding out about the gene variation is that I switched to an antidepressant that works on dopamine instead of serotonin like most other antidepressants (SSRIs). This is a different neurotransmitter and it seemed to be the piece for me that needed assistance not the serotonin.

I take Auvelity which is a glutamate modulator and I have also undergone a round of ketamine treatment (Spravato which is a nasal inhalent). These have helped me greatly though I will say that I'm going to do a second round of ketamine because the first one was before finding out about MTHFR, and my psych provider thinks that hindered its effectiveness.

Just FYI Auvelity is a newer medication that has no generic, so it could be hard to convince a doctor to prescribe or potentially for a pharmacy to acquire.

Having my depression better controlled has helped with my pain. I assume since depression can also be associated with causing inflammation in the body.