I worked out for the first time this past week (3 times), today my foot feels tingling and a bit numb, and my back aches. is it from the workout?

Probably overuse: Anytime you stress the body after periods of inactivity, you can overuse certain structures, ie: muscles, tendons, ligaments. This can lead to irritation and inflammation. Whenever starting a new physical activity, gradually increase how much you do each session. Light stretching before and after is helpful. Right now, rest, stretching, poss. antiinflammatories and possibly ice may help. Dr L

Pushing too hard.: I think you got it right. You might want to hold back until the symptoms stop. Try asking a fitness expert how to approach the exercise routine so as not to cause further damage.

Sounds like it: you may have a pinched nerve in your back