Hi,
1st, is Rectocele diagnosed by gastrosurgeon?
2nd u are having a urinary problems like uti and difficulty passing urine.
So very likely that constipation and urinary difficulty can be related to common cause.
I would suggest you to get examine and investigated for it.
Investigation like usg abd(focused on bladder dynamic), mri of back and study of bladder dynamic will be required.
In young girls sometimes this can be functional without any cause and only behaviour modification can help solve a problem.
Next Steps
visit a urologist he can guide you further.