A few months ago I bought a used Cannondale Synapse. I've noticed that even on pretty short (20is mile) rides my ass gets really sore, more sore than it has on other bikes in the past. I'm worried that it may be too big. For reference I am 5'8". Long arms, normal legs, average torso. Is it too big for me, or do I just need to make some adjustments? Or should I try a different saddle?