MacBook Pro Won't Auto-Detect DNS Servers

Hello,

I've had some serious issues with my internet at my student residence, but I always seem to be able to solve those issues with a few hours of tinkering (nothing majorly technical). But I've realized that no matter where I go now, when I try to connect to a Wifi network (free @ a cafe, school, friends house) my iPhone 5 will automatically connect & work instantly, but my MacBook will connect to the network, but will have either no DNS servers, or ones I've entered for previous fixes of my home network.

How do I make my MBP auto detect DNS servers? I'm moving out of this student residence tomorrow so I'm not that concerned about losing these DNS settings, but no matter where I go to use the Internet, I need to go on my iPhone / friends computer to see which DNS settings the network assigned for them and manually enter them.

Any help? Seems relatively easy, I assume. I would prefer not to reset my MBP because of the amount of programs I have that I no longer possess the disks for (MS Office, Photoshop etc).

Thanks in advance!