As you know, I have atypical (flat scar tissue) Asherman's that covered 2/3 of my uterine wall. Of course my lining in the other 1/3 of my uterus was always going to get stuck around 5 to 6mm, despite using Viagra, drinking raspberry tea, doing acupuncture, etc.
I will say though that before the miscarriage that caused the Asherman's, things like Viagra suppositories and acupuncture did help considerably, and I never had a lining less than 9 or 9.5.
Okay, so before my last transfer, when I already knew about the Asherman's and knew the Viagra and acupuncture would not work on me, my RE suggested being on the estradiol for one month. He said that's pretty much the limit (otherwise the endometrium gets old and less hospitable). I have taken estradiol valerate injections and used patches in the past to no avail but this time all we did were the estradiol tablets, given vaginally three times a day. I don't remember the exact dose but I think it was 6 mg daily per vagina. That's a pretty high dose for a non oral administration -- remember that oral doses are always much higher than other routes of administration because the liver chews up most of it before it can get to the uterus. After one month, my lining was up to 8.5! Obviously this was deceiving because it only was measuring the 1/3 of my uterus that HAD endometrium, but the u/s cannot tell you that. Interestingly, I had implantation, the first and only implantation in 4 years of doing multiple DE transfers. It was a good implantation too, with high betas. Unfortunately there was no fetal pole when all was said and done.
So my advice to you would be, yes, drink your water, your raspberry tea, consider acupuncture and definitely consider Viagra, and think about prepping your uterus for 3 weeks instead of the usual 10 days or so.
I had a friend who had a myomectomy and she noticed the exact same thing that you did. Viagra and acupuncture helped her a lot.