Thanks for the query.
sensation of the abdomen can be seen as side effect of the mirena
And there are no proved evidences related to weight gain due to the coil.
But as you are having congestion spots, better to consult gynecologist once and get examined to rule out serious complications like blood coagulation problems.
Don't worry these are rare but better to rule out.
If you are continuously having problem with this better to choose some other contraceptive
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429