Bad chest pain in pregnancy can be the sign of a pulmonary embolism, which is basically a blood clot in the lung. It may not be that, of course, but a pulmonary embolism is common in pregnant women (even young women) and can cause sudden death, so I really think you should go to an e.r. immediately. There is a simple blood test that can look for evidence of a p.e., and they can also do a harmless ultrasound of your legs to look for evidence of a blood clot (as the clot would have likely started there). If they find evidence of a p.e., they can treat you with medication that won't harm the baby. I went through these tests about 8 months ago for chest pain while in early pregnancy. It turned out I did not have a pulmonary embolism, but the doctors took my chest pain extremely seriously and would not let me leave the building until we had the test results. I, of course, was only worried about the baby, but had to agree with the doctor's statement: "Your baby won't survive if you drop dead." I later miscarried, but that was for totally unrelated reasons. So don't ignore your chest pain! I wish you the best.
The reason I said to drink water is for dehydration, because it could be preterm labor. If this is the case, lay down on your left side as well. But first, call your Dr!
It could be a sign of pre-eclampsia. I would call your doctor ASAP!! Good luck.
Call your OB! Drink water!