Knee pain. Can it be a lower back issue?
 

Haven't had any knee problems since I started cycling. 2 weeks ago we did our usual Tuesday night ride and I was really happy with my fitness and speed. Got home and both of my knees hurt on the backside of the knee one the outside of my leg. I'd been having some lower back problems that I assume come from sitting at work all day. Anyway since then I've been off the bike worried that I was getting tendonitis but its not gotten better and I've been having burning down the back of my thigh and butt. Could it just be sciatic problems?? My knee doesn't feel injured and the pain is dull and burning like the rest of the way up my leg. Also my knee only hurts when the sciatic problems are present. Otherwise it feels normal.

Do a search on the web for IT band stretches. They will cause both knee and lower back pain.

Do you stretch? Many times knee and leg (and even lower back) pain can be caused by tightness. Tightness leads to bad posture and poor ergonomics.

It could also be an actual injury, so if it's very painful I would see a doctor. But try and stretch first and see if that helps (specifically your calves and hams).

Check your cleat positioning too. When I have mine angled differently, my knees feel it right away.

All the above and stop tucking your legs under your chair at work. That has been my relief from the same problem. IT band stretch, straighten out the cleats and keep my legs extended more when sitting.

+1 for IT band stetches, a foam roller help for this.

I haven't tried a roller yet, but I hear they are fantastic.

No idea what your problem is but the first two photos below are a great stretch. Do it on a table or whatever is the right height for you until you can lean forward and touch your nose on the table. Great stretch which has had more impact on my cycling flexability than any other.

http://www.fortcollins-massage.com/gluteus-maximus-pain.html

If you want a lot of bar drop, yopu really nead to be able to do this easily

I stretch and do the foam roller regularly. Position hasn't changed in 3 years.