Ive had a dull ache in my left leg for about a week now, what could it be?

Believe or not, this pain could be caused by your shoes. Figure out what type of foot/step you have and try the shoe that is right for that particular style. This will give you better support in your feet, knees and back. You can take some anti-immflamataries to help with the pain for now or try a heating pad. Hope this helps.