What are some male enhancments that increase blood flow but only ones with real studies done and proof.?

ok before anyone blabs no nothing ever works like how i see the answears to most the other questions asked by guys like me. unless you got proof to back up its all bull**** scams please dont bother. im asking if anyone knows of any natural herbal brands that have studies and scientific data done that they do increase blood flow (dont care so much about size) other than stuff that can make you go blind like viagra. ewww nothanx. im almost 30. this just happened again for the 3rd time dunno what my problem is. before some of you ask me. out of shape? yes very lol but i used to be 50lb more and this didnt happen so its not that. all my antidepressents now are ones without the sexual side effects. so not that. last 3 partners i have been with i have had this problem. but the 4th ago i hardly ever had this problem. plus she was less attractive, jealous, and annoying lol so i dont think it is the girls fault. i think i can safely rule out it being meds, being out of shape, or the partners themselves. can anyone link studies to any brands that can back up there claims? but from the source of the studies themselves not published results from the pill manufacturers themselves on there websites. i think i just need more blowflow is all. i dont have total limp vd. just weak erections. works fairly well at the start just goes downhill later. ima start workin out some more but still an extra hand would help. i can get myself off but even still it can be harder or softer its random on that. im done having sex until i get this fixed =( can anyone please help me?