Swelling in the hip region after lifting heavy tile. What could it be?

Hi doctor,

First, let me clarify that I have been to a doctor for this problem already. But, the clinic is closed right now and I will not be able to get the diagnosis for a couple of days. But, waiting without knowing the cause is troubling me. So, I am asking for my peace of mind and also to have a second opinion. I lifted some heavy boxes of floor tiles a little over a week ago. Since then, I got a swelling to my left side between the hip and ribs and to my abdominal area. My doctor noted that those areas felt hard and said it might be fluid buildup. I am done with my x-rays now, but do not know the results of it. The swelling has not gone up or down since then. There is no pain, but sometimes there is a pressure, as if I am wearing a belt too tight. The swelling is most obvious when I stand. When lying down or wearing pants, it looks almost normal. Bodily functions have been normal. I do not have any diarrhea, unusual stool, vomiting, and so on. What do you think it could be? Thank you for your time.