How do i know if ive been over-exercising?

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.

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!

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!