Chest pain with one crutch

Dear Community,

I recently had a hip replacement, now 6 weeks in and using one crutch on my left side. For the past week I have been waking up in the morning with discomfort and a deep dull ache in my left chest area, actually feeling like it is under my left breast, in my heart region which I have found worrying. It only comes on during sleep when I wake up about 3am for the bathroom. It then persists. Feels very heavy and dull and right in my heart area. I was concerned it was a heart problem, or lung problem, but I feel tension when I fully breath out and expand my chest. I have no discomfort on my right side. (I use my left crutch during the day, but both crutches for when I walk outside). I was then wondering if it could be caused by muscle strain in this region. I realise that using one crutch, especially if I am using it slightly incorrectly could impact and strain the muscles in my chest that normally do not get this type of pressure. I am holding out to go to the doctor, as I have been concerned there is an issue with my heart. Also after getting up and moving around in the day it goes away. I wondered if this was an issue anyone had also experienced? Thank you very much for any thoughts.