What you are going through reminds me of how I felt last semester (also my first semester of graduate school). Other people would tell me, "Don't worry. You will be fine." - not very helpful for easing my anxiety!
It is definitely hard to concentrate on work when you have too much to juggle. Before I suggest that you quit your weekend job, I would like you to do a little research on temporary employment agencies in the area. I've used them in the past to find office work quickly. As we get closer to the summer months, I would recommend that you visit at least one or two of those agencies, register (bring a resume, not a CV), and tell them about your availability for work. One of them should be (at least I hope so) able to help you find temporary/temp-to-perm work during the summer and beyond.
Also, if you haven't already done so, clear non-obligatory activities from your schedule (e.g. graduate student committees).
Cal Newport's blog has more advice for students: http://calnewport.com/blog/
Good luck!