@Daniel Boone I am also a resident in your area. I have ridden the Gville-Hawthorne trail numerous times as well as others in the area. Aside from a little maintenance and better marking of distances and trail hazards that is a wonderful 30+ mile ride.
There are many solutions to changing the bar orientation. If you still have drop bars you can do what you are doing with some of adaptor used on the existing bar, but you can avoid that by simply using an extended stem (the quill on an old stem for higher height), and/or a shorter reach stem. Either option will straighten your riding position. There are also adjustable stems for both older quill and threadless ("Ahead" stem). If you have the newer threadless stem and it angles downward you can simply flip the stem over and that will lift your bar height without needing anything other than a wrench (usually 6mm Allen key). None of those options requires a new bar (in most cases). Other option is the bar itself. You can use a shallower drop bar if you can still get into a bit of an aero tuck, but if you cannot then a flat bar style or swept back bar style might be better. Those 2 designs are available in all types of variants some crossing between the 2 styles. Also, check your saddle height/position. It may be that lowering you saddle and/or moving it forward might help.
I worked in a hospital OR and also occupational therapy. Many small things can affect you and often getting your muscle groups in a little better shape can solve many issues. Regarding your exhaustion that might be a combination of variables. I would recommend avoiding the high heat periods even if riding on the shady Hawthorne trail. I recommend varied activities like walking, jogging, stairs climbing (avoid elevators if possible), and other activities that engage different muscles. Do not over do it, stay below the level of exhaustion or stop just past it, but not to a point where you are unable still function with ease. Starting out slow and easy and progressing from there is the key. Pain is a warning signal so heed it at all times and consult your physician if anything seems out of the ordinary. Also, ensure you are eating properly and getting adequate sleep. As always, when dealing with any medical condition you should consult your physician first before making changes on your routine to ensure there are no other issues. Sometimes a simple lab test can point out something that cannot determined via a routine physical.
If you see this riding around your area it is me. I ride all the trails and many roads in the area. The trails are all great for walking too as I do not find many, if any, cyclists on the non-paved trails.