I live in France and was given the vitamin E and pentoxifylline on prescription. I take it every day, no matter where I am in my cycle. That said, I'm not sure how good the evidence is for it. There are some studies showing that it helped to thicken the endometrium in patients who didn't respond to estrogen therapy.
I think that one of my next moves will be to ask my gynaecologist for a transvaginal ultrasound around the time I am due to ovulate and see how thick my lining is then. If it's still as thin as she seems to think, I'd like to try micronized estradiol and see if that helps. From what I've read, a thin lining is either down to poor circulation in the uterus or low estrogen. I suspect I may have low estrogen, and that the other stuff I'm taking to improve my lining may not help. I very rarely see any EWCM, which I think may be an indication of low estrogen.
Regarding my periods, I never normally get more than three days of bleeding, and it's always very light. I'm trying to be more scientific about it and actually measure the quantity of blood using a menstrual cup. Unfortunately I don't have a lot of data yet because last cycle was the first period after my miscarriage and I don't think my lining had a chance to build up at all before ovulation because I was still bleeding and spotting. When my period finally came I recorded 10ml on the first day, 7ml on the second day and 3ml on the third day, so 20ml in total. From what I've found on the Internet, less than 20-25ml per cycle is considered abnormally light. To confuse matters, last week I had a very heavy "period" with two days of proper heavy bleeding followed by three days of light bleeding. I think I bled around 75ml in total. I was really pleased because I thought it was maybe a sign that my lining had built up for once, and if nothing else that my uterus was having a good old clear out. It made me hopeful for the next cycle. But then unfortunately I tested positive for pregnancy on what I thought was day 10 of my cycle and am now dealing with what I suspect is another non-viable pregnancy and possibly an ectopic, so God knows what is going on. I suspect it will be a while before I start having normal periods I can track now.
As for the progesterone, from what I can make out it isn't usually prescribed in the UK because there is little evidence that it actually helps. But it seems to be quite commonly prescribed in France. I was originally told by one gynaecologist to start taking it as soon as I got a BFP, but she then referred me to another gynaecologist who has more expertise in miscarriages. When I spoke to her and told her about how I track my cycles, she told me to start taking it the day after ovulation because it might help with implantation. Interestingly, in Professor Lesley Regan's book, she dismisses progesterone supplements almost entirely, saying they don't improve pregnancy outcomes, but she does add that if any research shows they are helpful in the future, she thinks it will show that they help with implantation, and so would only be helpful during monitored cycles where the patient takes them during the luteal phase. So maybe there is something in it. Anyway, because I am self-monitoring my cycles I don't actually take it until 3 or 4 DPO, when I'm sure I've definitely ovulated, because I don't want to start taking it too early if I get a random high temperature and mess with my ovulation. I then take it until about 12 DPO and stop if my test is negative.
If you're being prescribed progesterone supplements and tracking your ovulation with OPKs and temping then maybe you could suggest this approach to your doctor. You'll need more progesterone if you're taking it in the second half of every cycle than if you only take it when you get a BFP, so they'll need to be on board with this approach.
As for whether it works, who knows? But I took it from 3 DPO when I got pregnant the third time and the embryo implanted very well indeed. So well that when I was diagnosed with a missed miscarriage it took two rounds of misoprostol and then an MBA to shift it. 
Unfortunately we didn't have the embryo tested because I passed the sac during the attempted medical management, but my gynaecologist thought it looked like a chromosomal abnormality from the ultrasound because the sac was very large compared to the size of the embryo. So it's quite possible that if the embryo had been normal the progesterone might have helped it go to term.
Sorry for the long essay. I hope some of this is helpful to you. I've only just created this account so I could start posting but I've been reading these threads for some time and I am so sorry about all your losses and everything you've been through. 