Thin lining....

Has anyone on here gotten a bfp with thin lining? My lining is always a measly 5-6. I've done 5 iui's. I had a chemical on my first natur cycle and everything else is bfn. Everything is perfect except for my stupid lining. Next month I am trying vaginal viagra to try to plump it up! I've tried RRL tea (thickened my lining up to a hefty 6.5) but then after trigger it went back some to 5.1. (Bangs head off wall). Vaginal estrogen didn't so too much for me either (always got me to around a 6 but delayed ovulation). Did anyone have success with a thin uterine lining or success with vaginal viagra? Urgh.