Pressure/ slight pain on the left side

So about 2 months I've had irregular periods but it's no my ovaries that hurt. It's closer to my ribs and it's more pressure there than pain. It's just noticeable and unsure what could be causing this. Sometimes when I lay on my back I feel or more kinda like a thumping feeling. What could this possible even be?I don't want to be going to the doctor over just something simple.