Im having pain in my lower back through my leg and to my knee to where it feels weak what should i do?

Get a medical examin: Lower back pain is quite common and usually settles down over 4-6 weeks. But the radiation of pain into your legs means a more severe injury(have you had any trauma?). You should seek medical attention and be checked by a physician ASAP. Also take some pain medicine(such as Tylenol/Paracetamol) while waiting to see the doctor.