Since it has been more than 15 months from your car accident, this is good news. It indicated that no major issue but pains and wane.
Now you are 7 months pregnant, this will further increase your weight by default for the baby sake. This is theoretically will increase the pressure on your back too and especially when you start pushing and even post delivery. ( These are possible expected consequences might not happen) .
It was not clear for me what is the soft tissue
, I may understand the hard tissue ( vertebrae and spine )... I need more clarification . The soft tissue or may be swelling on your back can be hematoma
( meaning collection of fluid or blood etc...) This is has to be attended by a specialist to find a tool o prove it or disproved . I do not think this swelling some thing bad..