A.S.
Hi, M..
My first child was a very poor sleeper for the first few years of his life. In time, it turned out there were some reasons for this, plus, some babies just aren't good sleepers. I would absolutely steer clear of a "sleep trainer." Some of these methods are just cruel. I recommend co-sleeping, to relax your baby. Also, two great books are The Happiest Baby on the Block by Dr. Harvey Karp and Nighttime Parenting by Dr. William Sears. Sears and his wife have written many books. Perhaps you have some of them. Good luck. It really doesn't last forever.
Amy