Very heavy belly and backache during week 28

This is my second baby and now in week 28 but already feeling very strained from my belly which looks huge and my back aches all the time. Sleep is also difficult because sometimes I have insomnia and sleeping on one side makes my pelvic bone very painful after many hours on one side. Still got at least ten weeks on and my mobility is already limited since I live on the fourth floor and have to climb the stairs on the daily basis. Anybody on second pregnancy and also experiencing huge belly around week 28 and terrible back ache