Maybe talk to your lecturers to see if you can leave class a bit earlier and arrive at your next class a bit later to ensure you have enough time to pump. I'm a university lecturer and I'd be more than happy to accommodate a student in that way. You could talk to your campus nurse, counsellor or student union rep to see if they can apply a bit of influence if you think your lecturers wouldn't be helpful.
Double pumping would speed things up a bit. If you're worried about the weight you might be able to rent a locker or have your campus nurse store the pump for you when you're not using it.
Like Missie Mack I have a Unimom Allegro and it's very light and easy to use. That said, I leave it in my office at uni instead of carting it back home with me each day.
Good luck. I hope you find the support you need to continue expressing breast milk for your baby.