I won’t say anything about your mechanics other than I agree with about everything that Roger has written.
As far as control goes he is right that you’ll need to practice, practice, practice.
Here’s an approach you might want to incorporate into your bullpens to help you work on your control. Once you are fully warmed up have your catcher set up with the target a foot off the outside corner at the knees. Throw 4 or 5 pitches to that location. Then have him set up a foot off the inside corner and do the same. Then have your catcher set up on the outside corner at the knees and throw 4 or 5 pitches. Then have him set up on the inside corner and do the same. After that work on your off speed pitches for a bit, then finish up throwing to a couple simulated batters and if your arm still feels strong you might want to then throw up to about 10 pitches for velocity, but be careful with that.
Throwing to simulated batters simply means pretending that you are pitching to a batter with the target being set where it would be in a game and the pitches being called based on the count. Don’t throw only fastballs though, make sure you throw an off speed pitch every third pitch or so at least regardless of the count. That’ll force you to learn to get your off speed pitches over and also will help you learn to switch back and forth between your off speed pitches and your fastball without losing command.
When you start getting a better feel for your location and being able to keep the ball at the knees or lower on a fairly consistent basis then you can also start working in the high inside and high outside pitches.
This isn’t anything I made up, this is something I found published in somebody’s workout plans on the net. Interestingly enough, I recently saw an article where a MLB pitcher, I believe but am not certain, that it was Jeff Suppan talked about doing a similar workout during his bullpens. I’ve been having my pitchers throw this type of bullpen for about 3 years now.