What do I do when it seems my mother is gaslighting me day in and day out?

You mention "gaslighting" in your profile. Can you tell me your own definition of what it is, and a few examples of how your Mom is using it on you?
Is mom suffering from Dementia? Does she live with you? Nothing to work with here and would love more information from you.

You didn't give any info, like your mom's age and whether you are her medical Power of Attorney. If you mom is not acting like herself or doing/saying odd/mean and uncharacteristic things, the first thing you should do is get her to her doctor and have her assessed for cognitive decline. This may explain a lot and give you an idea of what to expect and what to plan for. Please provide more info so we can help you.

Are there medical reasons your mom is living with you? How long has she been there? What sorts of things does she say that makes you feel like you are nuts?

Need more information. On the surface, you need to establish firm boundaries and a thick skin so her words do not effect you negatively.

Is mom a narcissist?