Hi, feeling of heaviness in the lower abdomen is common but however if its persisting then needs to be evaluated. Just check whether you have any urinary infection which can also have similar symptoms ( frequent urination
and lower abdominal dull pain). Probably because of sexual intercourse, you may be having pressure symptoms. Just wait for some more time, take a shower and if it still persists then meet your gynecologist.
Hopefully i have helped you.