@ThePurpleOne – you can never know what good effects your sincere efforts cause, so keep it up – don’t get discouraged just because it doesn’t seem to be working like magic.
Back in the day when a sibling was in shidduchim and nothing was going anywhere, Shir Hashirim was the segulah of choice (Perek Shira hadn’t yet made it on the scene). I was told by someone who had done it to follow a very specific formula – 40 days, same approximate time (mincha), and to say the tefilla afterward with the bakasha and to insert the person’s name after “sha’as ha’azanah” (leploni/s ben/bas plonis). [Naturally, I forgot one day and wound up doing it for more than 40 days.]
While shortly after the end of the consecutive 40 days, this sibling got engaged – which was really nice – it’s only now, after years of appreciating the beautiful shalom bayis that they have, that I regret not having tried it for more people I care about.