Here is a link to an online dictionary that specifically has the common abbreviations people use in Internet chat: http://www.netlingo.com/emailsh.cfm
(NetLingo, Dictionary of Internet Terms: Online Definitions & Text Messaging Acronyms). Also read the few paragraphs at the bottom of the page. If you can't find an abbreviation you are looking for, use the search box.
There is also a sticky thread on this forum entitled "acronym help" that has some abbreviations or links to websites with medical abbreviations
I have a pocket sized book entitled Medical Abbreviations: 15,000 Conveniences at the Expense of Communications and Safety
by Neil M. Davis which is probably in it's 11th or 12th edition by now that lists most of the common abbreviations used by medical personnel in medical record documentation. I purchased it when I was working as a medical coder because I was reading thousands of doctor's dictations of historys and physicals. Doctors have devised all kinds of abbreviations for tests, exam findings and medical diagnoses.
To tell you the truth, I sometimes can't figure out what some of the abbreviations mean that people use in their posts either. And, I've been a nurse for 32 years! You'll be learning (hopefully) to use abbreviations as little as possible in your charting for the very reason that one abbreviation can mean several different things.
Welcome to allnurses!