Help!

I'm trying to work on increasing my miles, and I thought I was doing it correctly. I've done a couple of 40 mile rides on a flat rail-trail. I've also been doing 25-30 miles on hills. Yesterday I did a 30-mile hilly day, and then today pushed out to 45 miles on flat terrain. I keep the cadence around 85-95. Now, tonight, my knee is killing me. It aches on the upper, 'outside', on the front - hard to describe where! It just feels close to the surface on the front. Right knee is fine, left is the problem. I've just started really putting in miles. Before two months ago, I was riding a flat 35 mile course every few weeks, but riding a stationary every other day.

Any advice? Please don't say to cut back the miles!