I got all fired up after reading your question because I've had my share of crappy secretarial jobs myself and I am all too familiar with these uncool shenanigans. However, there are a lot of people out there who are better trained in giving career advice, so I did a little research to find out what they had to say.
I found some of my information from the Monster.com job site. They have some good stuff on their message boards and you can always post a question for their Negotiation Coach. Or, check out all their forums. Here is a useful article I found about asking for more salary, as well.
One of Monster.com's experts said "it is now common for companies to pay new hires more than existing employees who have moved up in the organization. Merit increases have not kept up with what is being offered to attract new hires because of a shortage of candidates in certain fields." You must speak with your boss if you want more money, but you're going to need some ammo first. I don't think it matters where you got your insider salary info from. Research the market value of secretaries, check the Occupational Outlook Handbook and do a search on the net for salary info. I'd also look for another job with a better salary. Then you can go back to your boss to try to get him to bid for you using your job offer as leverage. That may be more effective and you may find a better job. Obviously, don't let them know you're looking for another opportunity.
Three months is really not that long; you're probably just out of their probationary period. But when you're ready to speak with your boss, wait for when s/he is in a good mood. Prepare a list of any accomplishments, improvements, or time/money-saving contributions you've already made. Then after you tell your boss how you really enjoy the work/people/environment and all that bullsh*t, you can show him what you can and have been doing for the company for the past few months.
Do convey your main concern as wanting to be paid fairly (and at a level that will keep you motivated) for someone with your skills and experience as it pertains to the job. Be firm with the employer your salary expectation (be realistic and reasonable) and ask the HR "is there anything he/she can do to help to make this work out".
At this point in time it would cost them more to recruit and train a replacement for you than it would cost them to increase your take-home a smidge.
Hugs and kisses,