Elevated heart rate

Rachel
Hi there!
​This is my first month TTC, and I'm on CD27.  For the last couple of weeks, I've noticed that my heartbeat has been elevated; it's normally in the high 60s/low 70s, but has been hovering in the mid-80s in the last week or two. I don't drink caffeine, stopped drinking alcohol several weeks ago, and I exercise regularly. 
Is this a possible pregnancy symptom, or do I need to be concerned? I've had some very mild lower-abdominal cramping (mild enough that I might be imagining it some of the time!) and had lower back pain yesterday, but nothing else of note.
​Thanks, all!