I interviewed for a job as a Human Resources Assistant that was posted on Monster. At the first and second interviews the job duties were explained to me thoroughly and the job seemed like a great opportunity. Since there are only two people in HR at this company, myself and the HR VP, I was told that I would also be getting limited assistance from the mailroom clerk and the receptionist.
I got hired and on the first day of work the HR VP told me that my job title had been changed to HR Manager and that they would be able to give me 2K more a year in 6 months.
I realize that the Manager title carries more weight but does that mean that I automatically deserve a higher income? I was willing to do the job under the title of “Assistant”.

Sometimes the title comes with more money, sometimes not. Depends on the company. In general an assistant makes less than a manager, but the company can give you a great title without any more money.
My husband worked for a company once that had a major project to determine what everyone’s title should be. They looked at responsibilities, outside contact, etc. Many people went to a higher title, but no one got a raise.
To answer your question simply, no.
You may be surprised to know that many people have others report to them (lower titles) who make *more* money than they do!
In general there is a correlation between title and salary, but not always!
You have been given a gift here. Many well qualified people would have applied for the job of the title had been included in the listing. Don’t quibble about he pay for six months. Prove that you deserve it and then be grateful, not greedy!
With only two people in HR, I think your boss should be the President and you the vice president. That way, as things appear to work there, both of you would be entitled to a raise.
Then, there is always king, emperor, etc. etc. to keep the ball rolling.
Being in HR, you should be able to answer this question. Don’t look a gift horse in the mouth. Just think if this job caves in for whatever reason, your resume says HR Manager. It is not uncommon for someone to get a title without monetary reward. They have given you fodder to ask for a raise when your 6 mo. review comes up. Your question shows that your are more interested in money, than doing a good job. Your question also shows that you are not qualified to manage, and I suggest you put your attention on keeping this job, not for getting more money than you interviewed for.