I can’t sing my own songs

I don’t know why, nor what it is that I’m struggling with but I can’t find the melody to my lyrics, i legit have no flow. I have no issue singing other peoples songs, no issue singing only with instrumentals and no leads, singing acapella in my own style but when it comes to singing my own lyrics i have no idea where to go or how to find the flow- it's like i need someone to tell me what it is first and that's upsetting. I don't know what the issue im having is nor what it's called but im trying really hard to find what it is so that I can fix it. I've tried humming, whistling, talking, writing along to a backing track, trying to find it in a backing track, i just can't for the life of me crack phrasing flow or melodies. I'm beginning to wonder if I'm tone deaf of something. What prompted this post is that I'm trying to write to this beat that I have but instead of finding the lyrical flow and vocal melody im subconsciously using the instrumental melody as a guide and it clashes and makes it hard to sing and it's just very frustrating.