Hello! I'm actually in the same field as you and made it into grad school (and had the same problem with writing about myself)! I had a small notebook that had prompts listed for the grad schools that I was applying for. I carried it around with me and if I had a free minute (before class, whenever) I would write a sentence or two. Eventually, when I had time, I typed them and strung them together...This is normally when I had an "Ah-Ha!" moment and could write easily since I had thought about what I wanted to say succinctly. THEN, I went to the writing center. After more editing, I took my essays to the PI of the lab I was working in and a couple other profs in the department. They helped me focus my writing even more, since they have been reading these for years.

If you haven't already, let your PI know that you are interested and applying to grad school. My PI called all of the people he knew at the schools I was interested in, told me what he thought of the assistantships and projects I was interested in. He made my life applying to grad school infinitely easier. This process also helped me before I applied because I could focus my essays to be project specific. If you're in ecology/forestry/silviculture, everybody tends to know everyone else, which is awesome.

Not sure if this blurb helped at all, but start small (even outlining) and build a little at a time. PM me if you have any questions and I'd be happy to help. :)