Just know that most doctors do not see a low-normal B12 as a problem. But at your age, it should be better. You really want to target your level to be at 500 and above. Know that B12 blood serum test are the least accurate way to assess a B12 deficiency. The good thing is that you don't need doctors to correct or even acknowledge it because you can correct it yourself. Don't waste your time trying to convince those who have dismissed it as an issue. Keep taking the methyl B12 and if you feel better on 2000mcg, then up it to 3000mcg a week later and follow that until you get to 5000mcg. This way you don't overload your system.

Add in the bio-available B complex at some point. Jarrow and Thorne make a good brand that has the right form of folate. Plain folic acid is not what you want.

IF you haven't done so already, correct your vitamin D levels.

It sounds like your issues may stem from the digestive problems. Even though you don't test positive for celiacs doesn't mean you don't have an issue with either gluten or wheat or both. The best way is to go gluten free and restore your gut bacteria balance. You may want to look at the celiac/gluten section on the forum. If you are taking medicines for GERD, they can and will block the absorption of nutrients, especially B12.

Even though it appears your symptoms came on fast (6 Months), it has really been going on for long time. Don't worry about the past. Just know that you can make the right choices to improve your health and wellbeing. It's not easy and it's not quick but you are taking the steps to restore your health.