TKR Low back pain post LTKR

I am 91/2 weeks postop, LTKR and have been experiencing low back pain when we go to town to do weekly shopping, but it is much worse the day after. Is this to be expected? I mentioned to PT and she thought I might be riding exercise bike too long, have cut back but yesterday we were in and the same problem. Did see chiropractor and she suggested asking PT for exercises to address this but I don't see her for another 2 weeks.c Any suggestions welcome.