Hello from JustAnswer.
It is common to get a muscle strain, and it can affect anywhere along the abdominal wall, including just below and to either side of the sternum. There are, of course, many other possible causes of pain in this location, but if it feels like a muscle strain and is tender to superficial touch, that is most consistent with a muscle strain.
An anti-inflammatory medicine, such as the naproxen, is a reasonable medicine to take to try to help with muscle strain pain. It also would be fine to augment the naproxen with acetaminophen. Other interventions that can be done at home include the local application of ice and moist heat. Ice is more important during the first couple days after a strain, and moist heat is more important thereafter. Wearing some firm clothing to support the area also may help, but we prefer to avoid tight support, such as from an abdominal binder, as it can impair deep breaths.
If this is not sufficient it may help to also use a muscle relaxer, but these are only available by prescription, so it would be necessary for you to be seen by your doctor.
If I can provide any additional information, please let me know.