What's wrong with me?

Sad story (warning). 
Hi ladies- I'm really concerned that something is horribly wrong with me. I'm 37 and around 35 and a half, DH and I started TTC. Our labs and blood work were normal. And my cycles were regular (between 27-29 days) and my AMH was 3.8 (normal). My HSG was normal and my GYN said I could take clomid to boost my ovulation. But I wasn't ready to go this route just yet. I thought I could get pregnant on my own. 
I started bbt charting in July 2016 and I noticed what I thought was a slow rise in my luteal phase. I thought this could've been the reason I wasn't falling pregnant. My GYN wasn't too concerned and was dismissive about my concerns. So I found a program online called conceivable.com that looked like it could help out my slow rise issue. The program tracks your bbt, diet, stress levels, etc. and delivers traditional Chinese medicine based herbal supplements for you to take during your cycles. I took the herbal supplements for almost 2 months and stopped when my period started to get messed up. 
I noticed in Sept 2016 that my luteal phase temps were lower than normal for me and my bbt dropped below the cover line. My period also was long, 43 days! I spoke with the program's creator and she was at a loss of what happened. Naturally I stopped the herbal supplements, but since then my periods have been long, irregular, and filled with spotting and/or breakthrough bleeding. 
What's most troubling is that I'm having long luteal hormone surges (sometimes over 2 weeks) so OPKs are worthless now. I just saw an RE to help get periods back on track and she retested my AMH. This result was 0.4, below there lab value lowest range! I called my mom to just talk about this and when I told her how bad this was she just sobbed. My dad died in late 2015 and I was hoping having a grand baby would help lift her spirits. I don't know if I can do this now. This makes me cry. 
How can my AMH go from 3.8 to 0.4 in a year and a half? Nothing has changed other that taking those stupid herbal supplements? I don't understand how I went from being ok reproductively to not within such a short timeframe. I'm terrified that I'm going into menopause now. I now have to wait to do a day 3 FSH and follicle count via ultrasound whenever my period starts to see what's happening. I'm so worried that my FSH is high and my follicle count is low. I don't see how it can be good given this new AMH result. 
I feel so stupid for taking those herbal supplements. I really thought they would help and not hurt me. I still haven't had a child, and I feel guilty that I probably ruined my husband's chances of having children. I just don't understand how things got so worse so quickly.
I just need some encouragement from others at this point. I feel so alone and I'm scared.