Suggest Remedy For Pain In The Back Behind Armpit

i had tentanitis surgeory 3 months ago after the surgeory about 10 hours after the back ok of my arm pit was hurting bad burning the pain is getting worse . i had a mri today waiting for the reading but was told they did detect fluid . the pain in in my back behind arm pit it hurts to put on a shirt coat etc...... the pain never goes away is constant to where all i do is lay in bed on heating pad and pain killers .