I was going to say your reach is too short, but you say you got a fit done? That early in a ride seems like an issue with your stem and/or bars providing a short or boxxy type fit on the bike. I am not sure what "flip it" means, but maybe flipping your stem over will stretch you out a bit. Hmmm...maybe just try and move your seat back. When you got fit, did they ask about your riding experience? My thinking is, they put you on something that you aren't ready for. It could just be a matter of time until you get used to riding.