There are a LOT of different brain tumors, ranging from totally benign to highly malignant. So getting that question answered is pretty critical. There is a lot of imaging (CT, MRI, etc) that probably will need doing, and possibly surgery. Treatments vary depending on the diagnosis; some are more effective than others, of course.
What would I do? I think while the evaluation is going on I'd solidify my low carb diet and maybe purify it even more of grains and possibly milk. I'd do exercise, but not chronic cardio (that may reduce immunity.) I"d be sure I had good family support around me and would try to avoid the temptation to not tell anyone to "save them pain."
I also personally would invoke a lot of prayer for myself and from my fellow church-members. Studies have actually been done on outcomes with prayer and the results are mixed with some showing benefit, others not much, but none of the studies have shown HARM. There are also some controversial studies showing improved quality of life and survival in cancer patients (we don't yet know if this is malignant, right?) who attend support groups so I would definitely ask about those.
I would also clean up as many stressors as possible, just unload the unimportant stuff as quickly as I could. I'd clean up my sleep hygiene, get on a good consistent schedule with 8-9 hours/night with little change in the sleep/wake times day to day.
I'm part of the "medical establishment" and would unquestionably pursue standard treatment, supplemented with the above. All of us in medicine have seen people pursue some alternative, have it fail, and then come back with a huge tumor and say, "OK, Doc, your turn." after it's really too late. Sometimes the initial tumor would have had a decent cure rate.
I hope and pray for a benign tumor in your case and a great response to treatment. It is scary and my heart is with you.