Hello Steph, Welcome to HealthcareMagic Forum.
I Would like to ask you few things here, so that i can suggest you better:
1.) Do you get pain during your shoulder movements?
2.) Did you sustain any Injury?
Your History suggests you have:
Kindly get yourself examined by a Surgeon. He/she shall examine you and do a blood work up including Complete Blood Count
(CBC) to rule out a Infection.
Once confirmed, your surgeon will drain it and Prescribe antibiotics. You will have to apply heat pads and use analgesics. Stick to your treatment plan and go for regular follow up. Avoid lying down on the affected side.
Wish you Good Health.