I second the suggestion to get a physical. 99.9% chance you are just out of shape ... but speaking as one of the .1% that was out of shape plus had issues .... better to know sooner, and react sooner.

If the saddle Really hurts, something is wrong. You might get a big fat tricycle saddle at a yard sale to use for the next few weeks, until you get used to riding.

i also agree that doing 10 minutes is fine. Try going more slowly if you need to. Getting going after coming to a complete stop and sitting for a long time can be devastating, particularly as we age ... after a while our bodies just stop trying. Up until mid-20s or so you can be sedentary and your body will keep growing and stay strong ; after that, your body will waste away (except your waist.)

Keeping at it is what makes the difference. I know from experience there is some point beyond which your body stops hating you for making it work ... and then it starts hating you when you don't.