In my experience this normally means the seat isn’t adjusted properly. Get a level and set it to 0° and give it another ride. If it still feels bad, make sure you’re sitting far enough back that your arms are stretched out, but not so far that your elbows are locked and that you’re sitting on the correct part of the seat. If you walk in most bike shops I suspect they’ll fit you for free too.
In my experience this normally means the seat isn’t adjusted properly. Get a level and set it to 0° and give it another ride. If it still feels bad, make sure you’re sitting far enough back that your arms are stretched out, but not so far that your elbows are locked and that you’re sitting on the correct part of the seat. If you walk in most bike shops I suspect they’ll fit you for free too.