If a lump has fluid in it, it's generally ok. However, when the fluid is bloody, it can sometimes be due to trauma, but the possiblitiy of tumor exists as well. So when a cyst aspiration returns bloody fluid, one has to decide how likely it is that the blood was from the procedure, or was there already. Sometimes waiting and re-aspirating makes sense. If it's still bloody, then at some point it needs to be removed to be absolutely sure the blood isn't there because of tumor. Ultrasound won't tell anything you don't already know: that the area is liquid. It won't tell why the blood is there.
Dear ollieboo: Since this lump (cyst) is causing you so much trouble, it seems reasonable to have it removed. He should not be upset that you asked a question. This is an important part of understanding your care. A mammogram should not necessarily cause the sort of trauma you describe. However, it is possible that it could have caused damage. Hopefully, your upcoming surgery will help to solve the problem more permanently for you.