Flat Feet after standing for short periods of time?

I just got a new job in food service management, after a month of unemployment. I find now that after an hour i start to get a aching pain in my feet that just gets worse as the day goes along, to a point where i’m taking 12-1600mg of ibuprofen to get thru the day. I started after doing a mainly sitting job(uber eats), so i’m not sure if it’s because i’m not used to it. I’m a 300 lb male, and i know losing weight can help, but i have flat feet and it’s really bothersome. Is there something that can help alleviate these symptoms? Please give me some good advice!