Can't know what it is, but there are some possibilities. It could be you strained your periformis muscle which is part of the hip complex but is above your buttocks. When it's inflamed you can affect your sciatic nerve, which runs over it. I got it riding a bike and can't ride one anymore, it just comes back. There are stretches for it. So that's one possibility. Diagnosis is really hard, it's by eliminating everything else such as pain radiating from your lower back or any number of hip problems. You could also just be fatigued from all that cycling and walking and toting heavy luggage around. Odd time to be on a world tour given the corona virus. Didn't know you would even be allowed to enter many countries. It could also be exactly what you think, and the cure would be to change the way you lift your luggage. When you travel the world, you don't usually take heavy luggage, you travel light because of this kind of thing. Backpacks are great. Wheels on luggage save a lot of wear and tear. Not taking a lot of stuff is what experienced travelers do to avoid this kind of problem. If it's from that, only rest will fix it, which would put a damper on your trip. Some stretching might help. Make sure you're getting sufficient water and electrolytes. But again, if you're right and it's the way you lug your luggage around, give some stuff away, only keep what you absolutely need, and alter the way you're carrying your luggage.