I remember heading down this road with DS1! The good news is he's now nearly 3 sleeps like an angel, bedtime is 6.30 (his decision, can't keep him up longer), up at 7, he still wakes in the night occasionally but only needs me once in a blue moon, usually if he's poorly.
The not so good news, I had to introduce a really quite rigid sleep routine for him:
Strict bedtime, upstairs at 6, bath, bottle, story (started at 5 months, he loved it), big cuddles until drowsy then into bed
Gradually phased the night feeds out by replacing them with water
Limited his daytime naps, never let him sleep more than an hour, ALWAYS slept in his cot. From 6 months cut his daytime naps to one in the morning and one in the afternoon. Never let him sleep after 3.30 pm.
We were really strict until he was about 7 months (so for about 8 weeks) then started to loosen up a bit (let him sleep in the car if we were out etc). It was really restictive to begin with but we saw the benefits in a couple of weeks and now he sleeps really well, is happy and active in the day, had good concentration and is a very contented little boy.
It worked for us but I appreciate the rigidness wouldn't suit everyone.
A friend of mine had similar issues are took the other route and co-slept with her DD to about 18 months.
Good luck it does get better