I'm having ongoing problems with fatigue - I'm just so so tired all the time.
Had a whole barrage of tests done which showed low B12 and very low vit D levels. Having B12 injections (initial loading doses and now every 8-10 weeks) and had an intensive 7 week course of vit D tablets too. I did start to feel quite a lot better but it's got worse again. 
Other tests have all been clear: thyroid, iron levels, calcium, IF and parietal cells came back negative, I'm not coeliac, liver function good.
Probably worth mentioning I am under quite a lot of stress, which dh and I are trying to sort out but there is no instant fix.
I'm just so exhausted all the time, finding everyday life a real challenge. If anyone has any experience to share or advice I'd be so grateful. GP is very sympathetic and says next step is repeat Vit D test (not easy to get on the NHS it would seem) and referral to endocrinology.