If the tattoo is healing well I wouldn't worry about an infection. If you start running a fever, have increased swelling in the area, puss coming from the wound, then you have something going on. Like Pid said, I might just be due to how you are holding your body. During this time of year a common cause of muscle aches and cramps is dehydration, so make sure you are drinking plenty of water.
Disclaimer: I am not a Dr., but I did stay at a holiday inn express last night. If symptoms worsen or don't improve in a few days, make sure to follow up with your regular Dr. and or your tattoo artist.