First Outing in 11 Days

I caught the flu at my workplace facility at the end of September, then caught a cold and it dragged on, so I couldn't go out at all. But starting today, I can work again. Until 2 days ago, I was dizzy and couldn't even stand, so I was lying down. I'll take it slow and do my best. Does it really last longer if you don't get the flu shot? Or is my immunity lower because I didn't get vaccinated? But the side effects of the shot...