Hi welcome to Health care magic forum.
Thanks for choosing H.C.M.Forum.
Your husband got an I.V.C filter fitted in inferior venacava to prevent thrombus
from his legs to enter into the heart, to prevent any thrombo embolism
Now he is having funny pain lower belly. that feels like a small round ball.
There are so many side effects some common are 1. fracture
of ivc, or perforation into duodinum.
Now it appears that none of these is the case. It may be the thrombus lodged in the IVC and causing obstruction to the flow of blood.Don't worry it could be a psychological feeling also.
What ever may be the cause any abnormal feeling should be reported to the concerned doctor. So immediately report to your doctor about this.
Wishing for a quick and complete remission from the complaint.