It could be scar tissue. Are your periods lighter? You could get a saline infused sonogram and hyfosy done to check for scar tissue and tubal patency. Would definitely recommend going to someone who specialises in Ashermans to rule out scar tissue though. There’s a group on Facebook around Ashermans.
I wouldn’t have thought it’s anything to do with a c-section but infertility after a pregnancy is common. Speak to an actual doctor and get some tests done. You can be referred if you are over a certain age and have been trying for over 6mths. Good luck :)