It's pretty natural. This probably is the worst period of it, because as you say the distractions have subsided somewhat, and the work probably isn't engaged or detailing enough right now to properly immerse yourself.
If you're not too far away then do think about taking a weekend trip home. Make a plan for one, in a few weeks, to give you something to look forward to. You can time this over reading week, if you have one, but try put it somewhere about half way during the term. Some of my flat mates went home a lot, and others not at all, so you just need to find what works for you.
There might be some support services in the union that can provide you with some advice, or even just someone who will listen, because they see it every year. My university has a confidential support group that you can phone, or just e-mail, a lot like Samaritans.