For you, assessing damage in the knee is important. Without Orthopaedician's visit and checking your tendon insertions and state of ligaments it is difficult to know exactly what damage you have done to your knee. After diagnosis, treatment gets easy. Take care!
I am having a similar knee pain problem. After walking a long distance 3 days in a row on a trip my knees began to kill me. Now nearly a month later my right knee is fine and left is still having pain. Like you I am only 24 and don't won't to have to spend money going to a doctor. Did your pain ever go away? Did you ever have your knees checked out?
I think this may be due to fatigue and due to the work you have put in. Rest, take anti inflammatory drugs and apply ice packs and see if your pain goes off.
There are orthopedic tests to determine if you have ligament tears which can be done by any physician . There is always not a necessary to go for an MRI. You can go for an examination as it is a chronic pain and there is suspiction that you might have damaged any ligament and it is always good to rule out injury if pain continues beyond 10 days.
For anterior cruciate ligament there is anterior drawer test and Lachman test. For posterior cruciate ligament there is posterior drawer test. for meniscus injury there is apley's grinding test and mc murray's test.