I'm 26yrs old expecting my third baby. I'm 25 weeks along since today I've been getting a stabbing sharp pain on my right side of my chest when I breath?

Talk to your doctor. While it maybe just a muscle or skeletal pain, it is important to consider and rule out a blood clot. Since these clots usually come for the veins in legs a safe test is to do a ultrasound test of veins of your leg. Please talk to your doctor right away.
See you doctor. Definitely see your doctor....Although there are many, many thing this could be that are fine, you really need someone to check your heart rate, pulse-ox (oxygen level), and respiratory rate. If all of these are normal, you will feel much better!