I think what may be confusing you is that you are assuming that NPC=Campus Panhellenic. The National Panhellenic Conference is the governing body for 26 member (Inter)National Sororities. For a complete list of all 26 groups, visit
www.npcwomen.org
Campus Panhellenics can be called different things at different campuses, including: Panhellenic Council (PHC), Panhellenic Association (PHA), Campus Panhellenic Council (CPC), Intersorority Council (ISC) etc. Campus Panhellenics include all of the NPC organizations on a given campus, and may include locals/regionals/other non-NPC social sororities if they are present on the campus and if that is how the campus wishes to govern them.
You're wondering about your eligibility because you think you can't be an initiated two Campus Panhellenic organizations. The rule only applies to members of the NPC. At your new school, you are eligible to join an NPC, and possibly a local, if they don't have their own rules about it.