Fixie / Road bike frame size causing neck pain? (Awarding max points!)?

I recently got a fixed gear bike for Christmas, but after riding about 5 miles I started feeling pain in my neck. I called the store it was purchased from and they only carry 48cm and 52cm bikes. Mine is the 48cm and I am 5'9" I can exchange the bike for the larger size but I fear 52cm is also too... show more I recently got a fixed gear bike for Christmas, but after riding about 5 miles I started feeling pain in my neck. I called the store it was purchased from and they only carry 48cm and 52cm bikes. Mine is the 48cm and I am 5'9"

I can exchange the bike for the larger size but I fear 52cm is also too small. So my question is, are both of these sizes too small for me? If they are too small what size do I need? and last, what if any advantages do I have with the larger frame vs the smaller one?

Thanks I will give max points to the best answer
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