Stuttrs can be helped by speech therapy. However, this can sometimes be really expensive professionally so you can try to adopt some of the same techiniques such as:
-Practise speaking out loud, and concentrate on the words you find you have most difficulty on
-Practising techniques to help calm your nerves whilst speaking
-Focusing on breathing, when to take a breath during speech etc.
As for lisps, you can actually improve these too. There are certain methods that are said to work such as smiling whilst talking and learning where to place your tongue to not make the sthh sound. Speech therapy and the above techniques can also help.
The Stuttering Foundation of America is a good source of help for stuttering. That is where our family of stutterers found the best information, referrals, and books, especially "Self Therapy for the Stutterer" and "Advice to Those who Stutter."
You should probably get your hearing checked out at the hearing clinic. Some people have speech impediment due to their hearing. They'd help seek you a speech therapist to help train you in your speech with the proper SH, TH, CH, S, T and such.
speak slowy to yourself in complete sentences and try to figure out which of your lisps occurs most on what letters or phrases. then sound them out in your free time(: this helps i used to have a stuttering problem
I wouldn't call it a disability.. but speech therapy is very good for training the lisp/stutter out of your voice. A stutter can't be completely solved, but it's good for all sorts :)
my cousin used to stutter A LOT but then he took speech classes & his speech cleared dramatically.
*sorry, a lisp can't be completely solved. a stutter, however, can.