Hi welcome there Inferno!!!
All I gotta say is its great to see someone else in Southern California, who’s going to college here and the same age as me!!!
Which college you going to btw? UC or Cal State?
Well starting off I’m kinda new to the pheromones but I’ve already learned a lot reading up.
For starters on your question to increase your confidence I highly recommend using Instant Shine!!! It gives people a boost by making them feel more opportunistic and upbeat! This can also help lighten the mood when others are around you.
For your second question, pheromones are not some magic potion that will make girls flock to you like your gold 
. Phermones are like clothes that will help enhance what you already have or help strengthen what you lack. Considering you work out I assume that your in pretty good shape, meaning appearance wise your probably off to a good start. For your shyness I recommend getting a pheromone that helps with your social experience. I would recommend Instant Openness which will help others be more inclined to talk to you. With this its on you to keep conversations going. Remember body language is also important. Now if you want a Phermone that helps you seem like an alpha male to others I recommend Instant Gentlemen, which helps promote a respectful nice alpha male! If you want something that’s well rounded try AMMO this product has 3 main human pheromones all balanced out so it helps give you a sexy attractive vibe, but like mentioned before clothes and body language have to work with this vibe.
Anyways make sure you read this
As for scents changing when mixed with colognes idk I haven’t tried mixing scented with scented.
Well anyways nice meeting you and GL in college!!! Hopefully when you recieve your GC you can get started on your way