Thanks for the query.
Rarely side effect like fibrosis
around the implanon
or development of infection etc can occur.
The lump you are feeling could be swollen lymph
So you once consult gynecologist, get examined.
If the presence of infection is confirmed you may need antibiotic course and anti-inflammatory and analgesic
Possibly with this the symptoms will decrease.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429