Betta Fish: Adopted a sick Betta looking for advice

I adopted this gorgeous boy today! Unfortunately I belive he's unwell he was laying on his side in the store. The owners had him in the back. So far in my tank he's been a bit lethargic and has been really twitchy. He's been laying on the bottom alot as well. I'm using Indian almond leaves and stress guard i'm just unsure if this is enough or if I should use medicine. I'm not sure if he's actually sick with something or is just stressed from being at the store in a cup. Just looking for a second opinion