First time low B12 and folate

I'm right at the beginning of all of this so I'm hoping to get some moral support

I went to the docs on Monday for an asthma attack and ended up having an emergency blood test. It came back as my B12 at 141/ngL and folate 3.1/ugL. I had absolutely no idea I had a deficiency, looking back at the last year I have felt more tired but I thought it was one of my existing illnesses. I'm really surprised by it all

Reading in here it seems like 141 is very low but I don't know if my doc is taking it seriously. They think it's my diet and they've booked a nutritionist to look at what I eat (I eat loads of B12 foods). I've got another blood test in 2 weeks but I've not been prescribed any injections etc

Posts here seem to say it's an uphill battle with docs, is it really? I feel like they're going to get hung up on this diet thing and if it's as low as I think it is I'm obviously pretty nervous about the long term

I think at the blood test I'll ask them to test antibodies from the advice I've seen, is there anything else I should raise?