>>1747526be wary of what you read on here, lots of bad advice and trolling. a good cycling posture isn't upright like what a non-cyclist would think, you're supposed to have a strong core and hold your upper back in a closer to horizontal position. just keep riding, you'll start getting stronger in a matter of a week or two.
here's an extreme example of what happens when you have more money than sense, the bike obviously looks ridiculous and the owner should just git gud instead of assuming the problem is with the bike:
https://www.youtube.com/watch?v=Akmd5ud4CYo 