B12 deficiency?

I'm like a part time vegan, so Im vegan 5 days out of 7. However, when I do eat dairy or meat I feel the effects of it IMMEDIATELY (more so dairy than meat). Anywho, about 1-2 months ago I bought B12 vitamins because my mom told me that if I'm gonna do this vegan thing then I have to take these vitamins or else I'd get sick. But I thought she meant like later down the line like when I'm in my 40s or something. After being vegan for about 1 month I started getting headaches so I bought the vitamins & the headaches went away. However, I only took the vitamins for about 1-2 weeks because I felt like I started feeling sick when taking them. So I stopped. However, sometimes my body gets crazy and I start to feel really bad and my body craves for meat. Well this past week I was a full time vegan but on day 8 my body started rejecting veggies & had an extreme craving for meat again. This seems to only happen when I go without meat for a long period of time. And the cravings are different from your typical PMS or AF cravings. It's like my body starts to reject everything other than what it wants at the time (meat) and I start to get nauseous as h*ll. Could I be suffering from a b12 deficiency? The pills make me sick but not eating meat for a long time makes me sick, which is partially the reason as to why I'm a part time vegan now because I don't wanna make excuses guys because I'm all up for the challenge but idk if my body can handle the vegan lifestyle. Is this a thing or do I still just have adjusting to do? I've only been vegan for 2 1/2 months now. I don't feel like these things should be happening this soon. And I don't have a scale but it is quite visible that I've lost about 7-10lbs ever since I've gone vegan. Is that normal? And I am eating enough, trust me! lol