Last week, beginning on tuesday evening, I experienced a tight, intense pain on the left side of my chest , towards the bottom of my breast near the sternum, it last about 2 hours and made it painful/difficult to take deep breaths, yawn or swallow , but gradually went away. this occurred again for a similar period of time the next night, and then again on thursday night. Today i woke up with a very tight and sore left calf . I ve heard these can be signs of blood clots, but I am an active 19 year old female.