Sore Back

It's certainly possible that your seat adjustment is causing your back ache. Keep in mind that when you raise your seat you also move it backwards due to the angle of the seat post. Therefore you've now increased the reach to the handle bars. You've also increased the drop from the saddle to the handle bars, further increasing the reach.

So while the new seat height might be correct, the longer reach it caused is the source of your problems. Just speculating, of course.

Keep in mind that if you move your seat forward, you also shorten the seat height as it relates to the bottom-bracket.

Now, it's possible that the new position is actually a very good position. You just need to acclimate to it. I take it you felt good while you were on the bike. If you think the position is fine, then work on hamstring flexibility. Tight hamstrings will put tension on your lower back. Also, be sure your rotating your pelvis forward. A common mistake is to bend forward at your waist with your pelvis rotated back. Again this puts added tension on your back, and with a slightly longer reach and drop could be what's the cause.

Hopefully this makes sense and gives you some places to look.

scott