hi.. i really sympothise with you. My second boy is also nearly one.. and for the first 9 months of his life he screamed!! I was the same and took him to the docs/ health visitors, sure there must be something wrong and of course... nothing!!
in the end i got to the end of my tether!! i liturally checked he was ok (clean, not hungry etc) then put him down and got on with what I was doing.. he screamed for about 40 mins (I was obviously with him the whole time to check nothing had gone wrong) as soon as he stopped i picked him up and gave him loads of love. the next time it was reduced dramatically!! it really didnt take long at all for him to cheer up!! honestly now he is the happiest little fella and enjoys his life!! (and I do to!) he was bad at night too.. so we did the same thing. checked him.. then left him.. it really did take 2 nights.. now he sleeps through..
Its really hard to do at the time.. but trust me its all worth it.. and its so much nicer to hear laughing than screaming..!!!
good luck with whatever you do!!