SPOILERS!

My issue is that at the beginning I rejected the idea of becoming a Vampire Lord however, before you enter the soul cain world or whatever I chose become a Vampire Lord and now after collecting the elder scrolls and crap I can't talk to Isran, all he says is to leave. How can I fix this, is becoming human again really my only option? I wanna stay a vampire lord! D:

Yes, it is your only option. http://www.uesp.net/wiki/Skyrim:Rising_at_Dawn#Detailed_Walkthrough.

And ask a mod to move this thread to the spoiler section.

You can always become a Vampire Lord again... Just ask Serana.

Unless you cure her of course.

You can't be apart of the Dawnguard and be a vampire. You have the option of becoming one on the dawnguard(still doesn't make much sense) side, but if you stay they will refuse to talk to you until you get cured.