Definitely do something about it ( ESPECIALLY if it was 3 times in one day). Don't let it go unattended to, because it can get worse. A half of a cup deserves some attention, i would call my doctor at the least if i were you.If you can't get in touch with the doctor, then go to the emergency room, because if it were to get worse, you want to be in a place where they can help to stop it . I had about a half of a cup one night when i was laying down trying to sleep, and just coughed it out and lay back down and went to sleep. The next night, i had massive hemoptysis, and had to call 911. I'm not saying this to scare you, i just want you to know it shouldn't be taken lightly. Who knows.... it may never happen again, but at least let your doctor know and have a plan of action should you need it. let us know how you are doing.