What does the doctor who performed the C-section say? If you haven't returned to consult with him, you must do that...or else your regular internist or OB-GYN.
I think to be on the safe side you should get the lump on the lower part o fyour right side of your stomach checked. It may be nothing. However only a health professional can tell.
You need to make an appointment to see your doctor or the gynaecologist if you are still under his care.
It is likely that you have a cyst and you may require an antibiotic or may need to be drained.
Your doctor or gynaecologist will advise you what will need to be done, if anything.
Let me know how you get on.
Best wishes.