Betta not eating/swimming

Hello! I’ve had my betta for a little over a year and a half now. For the past week, she’s been laying at the bottom of the tank and not eating or swimming. She’ll swim up to the top for air but then sink right back down. She almost seems like she’s swimming on her side.

I’ve researched what to do for possible SBD and tried fasting. She’s not eating anyway so that wasn’t an issue. Tried the pea. She wouldn’t eat. I do regular water changes and have a good filter and live plants, and I’ve been doing some daily water changes with distilled water. I lowered the water level of the tank too. I test the water regularly and the only problem ever has been the hardness. But it’s never been an issue until now.

Is there anything else I should be doing?? Any suggestions??