Just being a beginning runner can be painful enough, as your body tries to catch up with, and adapt to these new demands, but a precipitous increase in exercise time and mileage, such as what you just began, is almost guaranteed to hurt. I know that's a run-on sentence, but the concepts need to be considered as a cohesive whole.

True, there may be some tie-in with previous trauma to the knees, but even that can be partly and residually psychological. Painful memories can die hard. Ain't no faking the effects of a sudden increase in workload, though. Seasoned runners may not consider these jumps to be very large, but they can be.. for a non-seasoned runner like yourself.

The general rule of thumb is not to increase time, distance or intensity all at once. Limit yourself to increasing just one of these factors at a time, and to doing it in smaller increments than what you just attempted (eg: 25 to 30 mins one week, or the extra half-mile a couple weeks later). When you cross the line, your body will say no, and that may be what is happening now.