Could be any number of reasons. Without having before and after video or just after video one can only guess.

Before this summer i was a speed dominant bowler. I was throwing the ball around 17-18 mph but now ive went to 14-15 mph. Im really confused to how this happened. Note that i had been working on being a lot smoother this summer. Would me trying to be smoother be the main reason.

Our body often translates the "smoother", that our brain suggests, as more controlled. Having a similar problem, I'd bet your armswing, as notclay implied, is no longer free, easy and reduced-muscled. It might be that you're tensing up muscles that were freer before and your muscles are controlling and smoothing out your hand and armswing.

You can be smooth without being muscled. I'd also be willing to bet that your shoulders are preventing as high a backswing as you used to have.

True, none of this can be verified without a before and after video, or at least an after video.
Any chance of asking a coach you consulted before or a bowling friend with a good eye to see if they see anything. It does take a practiced eye to see something like this.

This is why i don't stop bowling for the summer. 

From my experience, the easiest way to control ball speed is by where you start your approach.  Start closer to the foul line and the ball will go slower.  It's simple physics.  Start near the back and the ball will go faster.  You can do other things, but this is the quickest way to do it during games and tournaments when you need to adjust speed to get your ball to react at different distances down the lane.