Hello and thanks for the query
The abdominal pain
may be related to the back injury
. As you have described the bruise is increasing and paining, you must to your doctor and check out for any hematoma inside or minor fracture.
If you have any fever or pain in lower limbs while movements that it is urgent.
Can take analgesic
and anti-inflammatory drugs like Ibuprofen
to reduce pain and bruise.
Hot fermentation also help in getting relief.
Take complete rest till you visit your doctor and restrict the movements.
Hope I have answered your query.