I believe you’re experiencing a posterior vaginal prolapse, which is essentially a bulge of tissue protruding into the vagina. This conditoin occurs when the tissue separating your rectum and vagina weakens or tears, allowing the rectum to bulge into the vaginal wall. Another term for this condition is rectocele.
Regarding your use of topical steroids on the vulval skin, it’s very unlikely that this treatment is causing the symptoms you’re experiencing. The symptoms are likely related to the prolapse itself.
I highly recommend seeing your doctor for an assessment and to discuss possible management options for the prolapse.