My body is constantly in pain and shaky but I have only gained 4 pounds..

I am 28 weeks and while I started out a pretty thick girl I will admit I had always kept a fairly flat tummy. I have a definite bump now so I'm thinking that could be why my back hurts so much but everything I read talks about how my body is coping with weight. I've gained four pounds total this whole pregnancy. I have been heavier than I am now before in my life. And yet my hips feel unstable and painful as well as my ankles and feet. I'm 5'8 so being a thick girl I have never been light and even at heavier weights I just never experienced aches and pains. So obviously it's not my weight. Watching my weight won't help aches and pains But what else can I do get some relief?