Why sudden drop in serum B12?

Hi everyone.

Just looking for some thoughts on my bloodwork. Here are numbers from my last 2 blood tests.

April 7 2020
Vitamin B12: 294 pmol/l (has been around the 300 mark for years)

May 15 2020
Vitamin B12: 250 pmol/l

Any idea why my b12 would drop 50 points in 5 weeks? I am experiencing pretty bad anxiety and depression since March and have been eating only one meal a day due to lack of appetite. Probably only 1400ish calories per day. 32 year old male. I also was very active the 2 weeks before my last blood test doing 8 hours of very physical labour a day. Taking no supplements containing b12.
Thanks for any input. I am just suspicious why my B12 would drop so much in 5 weeks?