Rash on hand after using up whole bottle of lotion. Why would it appear now?

Allergy? If you have been diligent with moisturizing your hands each time you wash, and your rash doesn't go away, you might have contact allergic dermatitis. See your dermatologist for an allergy patch test.
Allergy developing? It is not possible to say 100% but you may have developed an allergic reaction to the lotion. A delayed reaction can often be seen when someone finally develops an allergy to something. However, not knowing all the things you are contacting with your hands, it is possible this is something else.