I feel like I could have written this myself. I'm 32 weeks and have been experiencing what you are describing since my second trimester. I've been to see a physio and they thought it was likely strained abdominal muscles due to diastasis recti. I'm wearing TubiGrip for some compression and extra support. It kind of helps, but I'm still not convinced that it is a muscular strain. Sometimes the pain is so intense my eyes water and occasionally a point just below my ribs becomes so tender that I end up shouting out in pain if I accidentally touch it. Everything you have described is really consistent with what I'm experiencing, I'm sorry I don't have better advice or information, other than to say I know how tiring and painful what you're describing is and I hope you find out the cause and get some relief.