Swelling on thigh 25days aftr vaccinatio

My preterm baby ( 33 weeks 5 days) got her booster vaccine ( hexa 5- painless) and pnemonococcal on 4 oct. though nothing happened to her then, but now after 25 days she has developed swelling on her left thigh. Is the swelling due the vaccine or could there be any other reason like massage or anything else? Xray is normal, ultrasound says hematoma/abccess. She is currently on anitbiotics and painkiller since the last 5 days but there is a little diff in her. swelling . What do i do? Cant see her in pain. How long shall such swelling take to heal? Colour of the leg is normal ( not blue/red) but the swelling is too hard, such that she has completely stopped moving her leg. BW-1.786 kgs CW - 3.5 kgs