What Causes Stiffness In Shoulder Joint With Small Lumps On The Muscles?

hi im am a male 23 years old i have had a verry stiff shoulder joint for 2 years now and a massive lump has recently dissapeared leaving many small lumps in the muscles surrounding my shoulder ( armpit and inside the collarbone neck area . i am awaiting an mri scan to see what is wrong but this is taking some time and i am worried as doctors never noticed these lumps before and it seems they are spreading and i often get pains in an area thought by me to be my lungs as it hurts when i breathe, any ideas as to what this is? its my right shoulder..