sciatic pain (?) and swimming

Is it a good idea to swim if your lower back is pinching in sacro-iliac joint area on one side? Swimming is my mental health! But right now I can hardly bend forward, to right, or to left. Will be assessed by PT, but wondering whether anyone has had good experience swimming through back pain, or if this is likely to do me in. Generally I do core strengthening, shoulder strengthening, lots of onland exercises, but for some reason this pinchy pain hath appeared. Advice before I see PT? I NEED TO SWIM. Gracias. Isobel