Am I being underpaid?

I work for a small business (approx. 30 people). My title is Sales and Advertising Coordinator. I develop, create and place all the print ads for my company (I'm the only one with a Mac). I have been a graphic designer for about 4 years and at the current job 2 years. I make about 50K. I'm happy here... show more I work for a small business (approx. 30 people). My title is Sales and Advertising Coordinator. I develop, create and place all the print ads for my company (I'm the only one with a Mac). I have been a graphic designer for about 4 years and at the current job 2 years. I make about 50K.

I'm happy here but life happens and I now need more money to support my ailing parents.

I need to know realistically, how much do people with similar jobs make in the advertising industry. I like my company and my company likes me but they just can't afford to offer me more money.
Update: I live near Los Angeles.
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