Further to what Pandiarajan and Simhan mentioned, going by the general CTC ranges for .Net skills today, 6L p.a. is okay—unless you have other special rare skills or you are comparing with your friends who might be in larger companies. You could have given the reasons for your expectation of 7.5 L along with your posting.
Option II: Asking for Expected Salary
Your second option ["Can I ask my current organization to give my expected salary?"] has been answered by Simhan—it's too late. There's also a chance that your 'standing' in the present company is coming down, adding to your troubles.
Option I: Resigning and Searching for a New Job
Regarding your first option ["Can I resign the job and search for a new job?"], frankly, forget it. You would be bringing a lot of mental pressure on yourself, affecting interview performance in the process.
Like Pandiarajan mentioned, just focus on your present job—however tough you think it is, all it takes is some mental attitude. If a decision of yours can lead you to be so mentally disturbed, frankly, it could be tough going as you go up the ladder.
Just in case, if the reason for your changed thoughts happens to be any of your friends, I suggest keeping away from them for some time. Peer pressure is an awful (and surprisingly, quite prevalent) way of ruining one's career.
All the best.
Regards,
TS