If you work in Minnesota, you are guaranteed the right to have time to pump. It does not have to be a paid break to pump, but it is a state protected right. I believe KellyMom.com has links to each State's specific legislation. You also have the right to have private space to pump that is *not* a bathroom stall, so I hope no one has told you that you have to be relegated to the bathroom. The caveat to this is that if you work for a small employer, they aren't bounded by these rules - but many small employers will comply anyway in good faith.
Several people have already shared various ways you can increase supply. It is work, and will take dedication and perseverance, but, M., if this is something you truly want, you can absolutely do this!
In addition to the herbs and more frequent nursing/pumping schedule, I would also very highly recommend looking into attending LLL meetings, or at the very least finding some more support. In person is preferable since nothing quite compares to someone right there with you helping you along the way - but online works as well. There are lots of community forums available.
One such where you can get a personal mentor is http://adopt_a_mom.livejournal.com otherwise, there's http://breastfeeding.livejournal.com - a community of breastfeeding mothers who support each other.