What Causes Heart Palpitations With Either Exercise Or Rest?

I have had four kids. My mother has tachacardia and heart murmur and low BP. I am 31, 185, 5'6. Could never run very fast even in the military ( i was 18-24 years old). I could only run 1.5 miles 20 minutes at my best. I have heart palpatations when running, walking at steep incline, and when laying down doing absolutely nothing. I don't always get them when doing these activities but it also occurs with shortness of breathe sometimes.