Core can be pretty limiting for non-spellcasting classes, but if you want to get involved in non sneak attack melee combat as a rogue you'll probably want to multiclass. Sitting on D6s, light armor, and short swords is a tough limitation. Picking up 1 level in Fighter will let you use some decent 2-hander weapons and let you wear medium armor if you're ok with the armor check penalty and reduced speed. alternatively, a level in Barbarian will give you some much-needed maneuverability and a bit more hit points.

Realistically though if you want to have combat effectiveness as a core rogue, I'd recommend investing into UMD and casting some buffs and Tumble so you can flank. Sneak Attacks will give you plenty of damage output so you won't need to take Power Attack (and given your lower BAB it's probably better not to lower your accuracy any anyways). If you have a good enough Con, sticking with rogue will be okay, but you'll have to just play it safe and keep your HP topped off (False Life could be a good buff to open up with, and a wand of this will be cheap later on) in battles.