Bbt chart

Melinda • Had 4 miscarriages in 2015 and had our rainbow baby December 2016
I've been tracking my bbt since November (stopped a few weeks because I got pregnant but had an early MC). I've never understood it. I MC the 24th. Can anyone tell my by my bbt if I've ovulated yet? I found out last Friday that my levels were negative and we could start trying again. Glow has never given me a "cover line". Please help me understand. Thank you in advance.