My mouth actually goes down on the side's. How can I have a straight face w/out looking horribly miserable? I'm only 35. (photo)

Thank you for the photo and question.  It seems that a little Botox to relax the muscles on the side and possibly some filler in the corners will perk your mouth up!  Good luck!

Down turned lip corners treatment is two fold. 
1. BOTOX- There is actually a muscle called  Depressor Anguli Oris/ DAO that is pulling down your lip corner and making you appear in a state of perpetual pouting. This Botox treatment requires an expert injector. 
2. FILLER- Lip corners can be reshaped with fillers in the hands of an expert injector by not only injecting the actual lip corners but also injecting the chin to bring out the projection and reestablish better proportions.
The psychological effects of fixing down turned lip corners are amazing! When you look like you are sad, mad and annoyed, people respond to those "assumed" emotions and are confrontational towards you. But when you look like you are happy and without a worry or care, people respond positively towards you.You will not regret fixing your sown turned lip corners. But choose an expert injector for your work.

Hello, thanks for the question.  It would be helpful to see a picture with your smile, but I would consider Botox injection to the depressor muscles (DAO) on either side of your chin.  This would relax those muscles that draw down the corners of your mouth.