My now 8 week old is similar, but the sleep strike started a bit earlier. Her night sleeps are pretty good, but daytime naps are an absolute battleground. My strategies are:

At least one sleep a day in the sling.
Wrap her up and bounce on the fitball (this one takes mega-patience but it's good)
Hop into bed together
Wrap her up and chuck her in the pram.

I find that if she's had one good sleep already, then the next will be easier, and the next easier again, and then she has a good night. So right now she's in my arms, the next will be in the sling, then I'll probably tough it out and try for one in the cot.
Do whatever works!