in my left hand, i keep getting a stinging pain like a little bit below my knuckles, it starts stinging then goes away..

The only true way to determine if you have arthritis is to have it checked by a doctor and have some bloodwork done and possibly an xray.
Arhtritis of the hand is generally redness and swelling with pain in the nuckles.
Numbness in ones hands is generally carpal tunnel syndrome or a pinched nerve in your cervical spine.

well if the doctor takes blood for another reason would he be able to tell if i had arthritis.. or would he have to be specifically looking for it?.... because i had to get bloodwork not to long ago, my hands arnt really red but my knuckles show a little redness

They generally specifically request this. Does Rheumatoid arthritis run in your family at all? Or do you work in a position (if you work) that causes repeated use of your hands at all? Are they stiff in the morning and at night? These can be signs of various types of arthritis. Are any other joints affected at all such as your knees or hips?

If it continues I would go to my regular physcian and let them know your symptoms and they probably would do an ANA/rhuematoid factor test on you to see how things look. It is better to find out now and deal with it than to have to suffer not knowing.