What Is The Cause Of Aching Deeper Pain In Vagina During Intercourse After Childbirth ?

I had a baby 5months ago. My partner and I have recently started resuming intercourse. However, a few inches up on the inside vaginal wall I get a grinding sensation when my partner penetrates me. Its uncomfortable, also aching pain deeper in my vagina. My partner also says it feels different in there, he describes it as a clicking sensation. What is the cause of this? Thanks