I think the short trips & low-grade gas have a lot to do with it.
At the very least, please use at least a mid-grade gas, as recommended by MINI & what the engine was designed for. A can of injector cleaner & a decent highway run, if that's convenient, will also help to blow the cobwebs out.
It might help to turn the ignition on & wait for a second or two for the fuel pump to stop humming, then start it.