It can be really hard at that age (what am I saying? It can be hard at any age!)

Anyway, this is our story, maybe there's something here that can help

In the early months DS was very unsettled and hardly slept. From 4-5.5 months, however, things were very good after working through strategies in no cry sleep solution.
But, just before 6 months, this went completely out the window. We spent the next 6-7 weeks in a constant battle with DS to try to get him to sleep.
What helped...?
First, we gave up battling. If it wasnt' workign after 15 minutes or so, we gave up. no matter how tired he was.
I stopped counting his hours of sleep and number of wakeups.
Instead of waiting for tired signs, I waited for signs of complete exhaustion (it was only then that he'd give in to sleep)
We gave up on the cot and started sleeping him on a mattress on the floor. At first one of us would sleep with him, then he slept alone there.

I think our problems at this age were mostly due to separation anxiety. and also I guess he didnt' like the cot.

Good luck!

ETA - co-sleeping and/or slings could be a lifesaver in the short term