Do i tell my girlfriend im using pills?

So iv suffered from PE and ED for a long time (im only 29) and have recently got into a relationship. During sex, it usually involves me going down on her for roughly 30-40min then me being a 1 pump chump. This issue has been massive for me since teenage years. I have tried exercises, therapy, sprays and gels with no improvement. So i recently went to a doctor who prescribed me Taladafil 20mg. Now im both excited and nervous to try it, but if it helps and theres a big difference in the bedroom, should i tell her or not? A part of me says yes because i think lying or hiding it is i guess not nice, but in saying that, a bigger part of me wants to hide it for a while to see if anything changes and then maybe oneday stop it and see what happens.