The fatigue is unfortunately one of the main reasons why many of us had to quit our jobs. I'm sorry you're having to face this.
You do need to preserve what energy you have. Indeed, driving 4 hours is VERY tiring. You were with your boyfriend -- next time split the time coming AND going, and try to nap when you aren't behind the wheel.
When you have events like the summer festival, rent a scooter for the day. It's good you're renting a scooter for the Florida trip. When you're there, rest as much as you can. Excuse yourself from some activities and get an hour or so "down time" in the afternoon, so you can manage to get through dinner and the early evening. The heat and humidity will be very taxing, and combined with the "not home" location and the stress of the event, you're going to be exhausted afterwards.
When you check in at the airport, tell them you need assistance -- a wheelchair and a push -- to get through security and to your plane. They'll be glad to provide it (for free, but "tip" whoever pushes you!). Then when you're on the plane, about 30 minutes before you're scheduled to land, ask the flight attendant to call ahead and have someone there with a wheelchair to meet you, and get you through the airport, to baggage, and to whoever is picking you up (or your rental car.) I don't know if you've traveled by air lately, but they really aren't happy with folks moving about the airplane, except to and from the bathroom (and even then, you're looked upon with suspicion!) so you might find yourself with plenty of time for a nap on the plane, at least!
Summer festivals, long airport terminals, Florida trips, are NOT "every little thing" when you have MS. They are events that you need to plan for, need to know that you need to rest plenty, before, during, and after the event, and that indeed you may "pay" for it later by needing more "down time" than someone else who is 32...and who does NOT have MS.
I was going to suggest you find a way to reduce your hours, but you said you're only working part-time as it is. Can you find a way to conserve energy on your job? Sit down, work a few hours and take a break -- even 15-20 minutes of quiet time can help -- then work a few more hours? Do some work from home? Work from a wheelchair so you don't have to walk around? (I don't remember exactly what you do...so these are just generic sorts of suggestions...)
I really am sorry you're in this position.
...I am not a doctor, nor health professional, and don't pretend to be one, here.....