Seems to me based on what you wrote that you may be overdoing it, yep. Despite being a former athlete, the key word would be 'former' and you just need to work your way back up to 'current'!

Are you starting with the 10lb plates? Maybe you should start with 5's or with the bar only. No shame in that! Also, make sure your form is correct and pay attention to where your knees are in relation to your toes. It's a process and you just want to progress into the program w/o injuring or straining your body. In fact, you could even start out the squat portion without the bar and build up strength just by squatting your body weight. That may be something to try too.
In any event, good on you for pushing play. Don't give up, just be smart about it and over time your body will gain strength and endurance and you'll be back at athlete status!
Cristy