What we feel is about our own thoughts and perceptions on our experiences. You cannot know why things seem to have improved without asking them and seeing what they say; it may/may not have had anything at all to do with you, might be store-wide or a policy made throughout the company/multiple stores.

You do not have to forgive them but you miss valuable information not asking why they smile, since you feel you have become "a b*^&#?" Maybe they do not see your demeanor that way and just smile because they automatically smile at everyone. Or, maybe they are afraid and are smiling hoping you will stop looking the way you do. You cannot know if you do not ask/talk to them.

Do they know you want to be promoted (not everyone does)? I don't know what jobs there are but maybe there are no openings yet. I think you have to ask management when/if you will be promoted and let them know that you would like a different job.