Welcome @heidibgw, I have a similar problem that makes it difficult for walking due to having trouble holding my head up and keeping my body from being bent over. I've had PT that has helped some and try to work on my posture daily but at 82 that is kind of a challenge for me. Here is some information on posture that makes a lot of sense to me and hopefully will help:
-- Mayo Clinic Q and A: Proper posture and body alignment
https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-q-and-a-proper-posture-and-body-alignment/
Have you talked to your doctor or had any tests done on your neck or spine to see if they may have some suggestions for treatment?

@heidibgw
When I began to feel myself slouching & not holding my head up I first went shopping. At Goodwill I shopped around & found a small back-pack purse, put 2 - 5# weights in the back-pack, & shortened the straps so when I wear it, it rests High, about shoulder-blade height on my back. It's a Constant remainder to Straighten my spine rather than slouching. Then I constantly keep reminding myself to push my head back above my spine & tuck my chin in.
An Orthopedist once told me, 'Bad Posture invites bad organ function ... when you slouch & let your head drop forward you put strain on all the muscles from our shoulders to the HEELS on your feet! You cramp up & squeeze your internal organs into less space than they Need! Worst of all you're putting an
Un-Due amount of work on all those muscles from your skull to your toes! Eventually you'll develop a "Widows Hump"! This isn't how you stood or walked the First 50 or 60 years of your life, & You Wonder Why you have Aches & Pains all day long?'
Made Perfect Sense to me ... so when I go for daily walks, I'm wearing the back-pack, reminding myself to get my head above the shoulders & correct my posture to where it Ought To Be!
(That's my Story & I'm Sticking To It!!!)