Worried. Shortness of breath.

Kaitlynn • Ellie Sue. Born August 20th, 2017 ❤️
I'm 18 weeks and I'm very short of breath. I know it's normal during pregnancy but I feel like it's really hard to breathe. Especially when I lay down in bed. I constantly yawn and I feel like I can't get enough air. ☹️ Any position is just hard to breathe in. should I be worried? I'm going to mention it to my doctor next week at my appointment.