he isn't broken. I play as him sometimes and even when I'm not playing him I know how to go against him. Come to botlane their little butt if the first thing I'm trashing.
He's weak against champions who don't really rely on Auto Attacks.
Even tho I main bot lane where some AA reliant champions are... I got 3 skills to use against him that scale off AD.
As for shrooms. when you play as him you know all their usual placements. So it's easy to guess some times.
Next time you go up against him take a
than change to
at level 6 upgrade to
at 9.
Stay behind your minions at all times.
- Some teemos use shrroms to farm let's the minions take the blunt on the damage. So many people don't think a teemo would put it in the middle of the road but sometimes it helps with Wave clear and CSing.
Don't go into bushes a lot.
- Favorite places for teemo shrooms.
Don't entirely trust your path maker.
- Sometimes A teemo will use the fact that it makes the quickest way to get somewhere by putting shrooms near CORNERS (Well I do at least)
Lastly. 
- they costs 75 gold. put down 1 in a key spot where it wont be found but may be a teemo shroom hotspot.