Good news! At level 5 you actually are weaker, because everything actually got tougher because all your Martial Buddies just got Expert Proficiencies. Its actually extremely weird why its set up like this, but the theory I think is most likely is that third level spells are considered to be a big power bump.
Its actually the Worst Level in the Game for Spellcasters. 6 is almost as bad, but at 7 you'll be back to where you should be.
Hang in there.
At level 13, my parties Sorcerer (I'm the GM) consistently outdamages everyone, and not just against mooks.
Pro-Tip - Phantasmal Killer is a nuke now, and a darned good one. You're two levels away from it, but look forward to it!
Actually pretty good! It's a shame that I'm an elemental sorcerer so I'm stuck with the primal list, though. Any help with that one?