Shortness of Breath

This is my first time being pregnant, so I’m sorry in advance if this is a dumb question. But I noticed I’ve been getting more and more out of breath. It’s to the point where simple things like walking up a flight of stairs, pulling a few weeds, walking for 10+ minutes has me completely winded. I will note that I also had slightly low RBC and HCT at my last OB appt, so I’m wondering if this is contributing as well. But- is it common to be this out of breath in the 3rd trimester?