I have agoraphobia, and I can't say that I'm a professional or anything, just someone who has been where you are now. You are right in assuming that your agoraphobia and social anxiety was better because you were out of the house everyday during college.
I view my agoraphobia as wet cement. It will always be there for me, always a challenge, but the longer I stay in my home, my comfort zone, the more the agoraphobia 'sets' into a much harder wall of cement. By making sure to get out on a regular basis, I am able to keep my agoraphobia from taking over completely.
When I haven't been doing my part in getting out, it does take over. When this happens, I have to start over, with baby steps, slowly widening my comfort zone. Start by just stepping outside your house, in your backyard or your front porch. Sit and observe your surroundings. Do this until you feel your anxiety lessen. Next, expand your area by walking to the mailbox, or sitting in your car, etc etc. Next start making daily trips to any nearby store and just park, observe surroundings until you are relaxed, and go home. The next step is to actually go into the store. Go with a short list, or just window shop, walk among people for a few minutes, then return home. I think you get the idea
Of course you can customize your own plan. Do this at whatever pace you need, a few days at a time for each step if needed, as doing too much will just trigger panic attacks, as you have experienced.
You will deal with this for the rest of you life, most likely. It is important to keep it under control with daily management, much like diabetes. The good news is that the more you manage it, the easier it becomes, until it almost seems to disappear, but don't forget about it and stay home for a few days in a row, because its still there, just in remission