One reason for saggy skin is that minoxidil retains water under skin layers. If that happens, you may simply reduce the dose/dropper slightly and it will help a lot. Moreover, if you are working out or active, then saggy skin would not be a problem for too long, as water would be dried out.
In any case, buy Retin-A cream in prescription conc., dirt inexpensive on online pharmacies, and apply it on your face, specially the forehead area (which is closer to minoxidil ridden scalp, and thus more vulnerable). You will be so amazed that you would not stop looking at your skin in the mirror.