Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
Without the ability to examine you and obtain a history, I can not tell you what the exact cause of your symptoms is. However I will try to provide you with some useful information.
Your symptoms may be related to a vascular issue rather than a neurologic one. Specifically, varicose veins can cause a burning or pain in the feet and behind the knees that is felt less during movement. Most often, bulging veins will be visible on the legs. This is more likely if you stand a lot; treatment is with compression stockings, leg elevation, and sometimes there are injection or surgical treatments available.
At your age, disc disease (herniated discs) in the spine, or spine arthritis, is unlikely. However, if you were born with a narrow spine (called congental spinal stenosis), then you could have symptoms marked by pain in the legs during walking, relieved by leaning forward or sitting down. This is best diagnosed wtih MRI of the spine.
Another cause of pins-and-needles sensation is neuropathy, or a problem with the nerves of the arms or legs. This seems much less likely since your symptoms only occur for a few seconds and then resolve.
I recommend you discuss your symptoms with your primary doctor (pediatrician, family physician, internist etc) and after he/she examines you he/she can determine whether or not further testing is indicated.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.
I dont seem to have bulging veins so it doesnt seem to be a varicose vein... My GP says my symptoms are very vague and thought it may be potassium or b12 defiency. Currently waiting for the results of the blood test. Does anyone have any idea what kind of specialist should i look for since the problems still seem to persist? I'm wondering whether to look for a neurologist/podiatrist/chiropactor ...