I feel the same as you. I'm 17 weeks and feel I'm bigger than I should be, already waddling or getting uncomfortable when sitting for too long and slight lower back pain. I've just started yoga so I'm hoping practicing that will help.
Not everyone’s experience of pregnancy is the same, you can’t compare. Some people breeze through pregnancy whilst others struggle. It’s about how you feel not how someone else does, and you absolutely can complain pregnancy is hard- you are growing a person inside you.
Everyone experiences pregnancy differently. It really is such a unique experience and different bodies and hormone levels. I’ve had friends who have felt unwell or achy the whole way through. I was fortunate to feel pretty good last pregnancy after 14/15 weeks. Obviously try to eat well and keep some level of activity like even just walking or swimming if you have access to a pool or maybe a prenatal yoga class. I do think this can aid the body in staying strong for the changes. Posture can also really help, I know slumping into a couch feels good but there are some online resources about sitting more upright/forwards or even on a ball can help how you feel body wise. But some women can’t do anything as they are just so impacted by the change. This is completely ok. Rest is also important. And everyone carries differently. Also comparing to 8 months, you may only feel a bit different to how you do now by then. It’s your journey and you have every right to feel however you feel.