My tutor says he can't understand my presentations.

I passed the IELTS well but I really struggle when presenting in English. It's not just nerves as though I am nervous, I am usually a good public speaker. I know my topic and I understand the material but my tutor and class often say they struggle to understand what I'm presenting. Has anyone else experienced this? Does it get better with time, or is there something specific I should be doing to improve?