How do I know if i’ve been over-exercising?

Next day, how sore? Agree with dr. C. Also, how do you feel the next day? If you hurt [a lot] the day after you exercise, then you're over-exercising. Good rule of thumb: cut back your exercise by 50% [less time or less reps]. When you feel good the next day, you can increase your exercise. Congrats on getting out and getting moving. Good for you!
Discomfort. Discomfort/pain and tiredness in the body area subject to exercise will be your best guide to make decision to stop your exercise session.
Pain or fatigue. Too much exercise can lead to several problems which you need to be careful of. If your excessive exercise regimen is causing a chronic pain in joints or muscles, causing fatigue both physically and mentally, or causing a burnout mentality towards exercise, then some rest might be indicated. It is important to schedule recovery days into your program to avoid such issues. Rest is good!