More experience less pay
Part of the issue is that as you stay at a job over a period of time, you build innate knowledge that is somewhat difficult to reproduce in a new employee. So, with training time and mistakes, it makes more sense to pay a knowledgeable employee more than a new employee doing basically the same job.
If this career (certified medical assistant) is one that an employee can handle the basic duties after becoming certified, chances are you won't see more money because the talent pool for most of the jobs in the career are at entry-level.
You option is to move beyond the "assistant" level... maybe becoming more supervisory at a larger practice and having more responsibility (and more pay).
Another part of the response to your question depends on whether or not you're working now and how badly you need or want a job. If you're not working, you may not have a choice but to accept a job for less, assuming you need the income. If you have a job, you probably can afford to be more choosey and wait until an offer comes you're way that justifies moving. Normally, it makes no sense to switch jobs unless you can increase your salary by at least 10% to 15% - but, again, that depends in part on how badly you need a job. Which situation are you in at present?
Paul W. Barada
The Negotiation Expert