My bp has been consistently 110/70 since I got pregnant, which I think means I have always been a bit on the low side...but one week about a month ago, I had gone up to 133/78, and that was a bad day! Back down again now...the nurse told me 110/70 was not too low and not to worry about it but I've no energy for things like stairs!!!
But 90/45 sounds really low...take care of yourself!
Sue