Work on the bike fit. Very small changes will make a big difference. Once you get it right it's like magic.

Toss the gel seat.

Sit up and stretch whenever you feel any discomfort anywhere. Change hand positions once in awhile, even if just subtle changes. Slide around on the seat to slightly different positions.

As your "all day endurance" improves you will be more comfortable even without improving bike fit. Tired muscles don't give proper support on the bike and can lead to all kinds of discomfort. If you start feeling too drained take a break. Nothing like a little nap under a tree.