At 3 months how your breasts regulate milk production has changed. Instead of being the hormone driven "just make heaps" from the first few weeks, they now respond by making milk when they are emptied.
So to build up a freezer supply you need to keep emptying them! Pick a time each day when your DD isn't likely to be wanting continuous feeds (e.g. when she's usually asleep) and make that the time when you feed the pump. And over a couple of days your breasts should get the idea, and there should be more there.
Once you are at uni you will find that you have to express or you will explode. And what you express at uni one day will be close to enough for bub the next day - you don't actually need to stash a month's worth of milk in the freezer.

Tips to make expressing on the go a bit easier:
*talk to Uni - there may well be a Mum's room or a first aid room or some other relatively quiet place with a power point.
*beg, borrow or steal an electric double pump (or hire one) so you can halve the time you spend expressing
*get a few extra sets of "bits" for your pump (off ebay or off friends), so you can do a big scrub every couple of days.
*See if you can get access to a fridge anywhere at Uni. That way you can just put milky pump bits in a big zip-lock bag in the fridge and come back to them, rather than having to wash each time
*little esky with cold block will be needed to get the milk safely home.
GOod luck!