Congrats sa second baby! Yung slight cramping at heaviness sa puso ay pretty normal sa early pregnancy talaga, pero since you're already 6 weeks, it's really best to check with your OB para sure lang, especially if ito yung second time mo, alam mo na kung paano dapat feel ang normal for you. A few of my mum friends experienced the same at okay lang naman, pero each pregnancy is different kaya don't skip the checkup para peace of mind mo.