I doubt myself all the time?

help ! i am doubting myself in everything i do, even at work, i work in shop and i am petrified i have done something wrong on the till or put someones item or a refund through wrongly on the till, at work, i double check everything but when i get home i cant seem to turn off and worry if i have put things through the till correctly, is this low self esteem or am i worrying for nothing.