getting frustrated with my self

I am just extremely stupid, in school I could never see the white board and so i got my eyes tested in year ten {after years of begging my parents} and found out i had poor eye site, by then i was too far behind in school and always blamed it on that. After leaving school i jumped from job to job then went to tafe, but i left early because i couldnt keep up. After that i started to drive and noticed i had no sense of direction at all, and no matter how hard i tryed i couldn't get my lefts and rights . Now i have a job i really love [working in childcare] but to keep my job i have to do a tafe course, i do all my work and hand it in on time, but my tafe teacher asked me if i had a learning disabilty, I obviously replied no and felt extremely insulted. but Honestly i don't know, I keep spacing out so even writing this has taken ages. Right now im 18 and havent been to school for over 3 years and i dont know if im dislexic or just generally stupid
I now just laugh off my bad marks with my friends and they think its because i don't try, when i really do its all just starting to stress me out now finding my self estemm at a new low, and getting fustrated with my self to the point i just start crying.