I think that sounds like a good dose of soy given your cycles can be quite long. Hopefully it will regulate ovulation, that is if you don't get pregnant first cycle on it.
I ovulated right on time, so it didn't adversely affect my cycle and mine is 27 days.
You could have something minor like a polyp, I was told these act like an IUD. I had one which went by itself which was completely terrifying since I haven't seen one before! But it was completely painless.
I don't know what those scans are like, I'm told they can be uncomfortable, the HSG anyway. You could ask for a mild sedative if you wanted