Here’s a revised version of your message:
"I’m not sure how to articulate my problems, but I will do my best. I've been feeling unwell lately, and despite trying various ways to help myself, I haven't seen the positive outcomes I hoped for. I've been seeing a therapist, but it feels draining, and I’m so exhausted that I struggle to sleep at night.
The real reason I returned early is that I was on the verge of losing my mind, but I can't share this with my grandmother or even my dad. I’ve been missing my mom a lot lately, even though she had a tough love approach. I understand that’s often the way strict parents are. She passed away not long ago, and I find it painful that I can’t remember some details about her.
I miss her, Thabang, and it hurts. I’m worried that my academic performance is slipping, and that adds to my pain."
Feel free to adjust it further to better reflect your personal voice.