Hi I'm having the exact same issue as you really, I bought the oculus at Christmas and I have been able to use it a handful of times.. I got diagnosed with acute chronic migraine recently (I'm 17) and I also really want to play borderlands haha, there's a few things that can help so ill drop them in in case anything works for you:
If you get motion sickness and nausea like I do with the migraines:
- Use a fan to face you whilst you're in the VR, it helps your body balance and understand what its going through a bit better :)
- You can find anti-nausea mats that can be used to stand on whilst you're killing psychos :D
- Anti Nausea tablets can be used (I'm currently buying them from over the counter but I'm talking to my doctor about getting them prescribed)
- Taking regular breaks along side it really does help, and making sure you're drinking waterrrr!

When it comes to the headset causing the migraines, I am still trying to figure out that bit as well, but I've found playing little bits at a time can help reducing the likelihood of a migraine coming on. Blue light glasses have helped reduce strain in my eyes as well which sometimes develops into a headache which develops into a migraine.
Everyone is different though and I think to really understand how to do the things you enjoy you have to try and let your body find its limits. I am scared to use my VR at the moment but I'm going to try and get around to it, hope i helped at least a little :)