sounds like a combination of mild depression and stress.

The symptoms you initially described are pretty much classic mild depression. comfort eating too???

stress can lead to sharp neck and shoulder pains as your muscles get knackered from constantly being tensed. For most people its mainly aches and cramps in the neck and shoulders.

worth getting a check up at docs and trying to increase your activity each day. You need a check up because if its that crippling pain that you feel weak then it might be something else especially as youve done your back in so need to look after your spine to be safe!