I'd personally start from sketch of basic shape (without those rounded undercuts), then revolve it to get a full bottle.
Next step is to add those undercuts, I suggest You trying to do it by sketching the trace and profile of them (use helix and spiral, and cut along the trace).
Next step is the shell tool to make a bottle from your solid brick.
About the bottle nect thread - use the helix once again, and add along the trace tool.
Last step is to add some round to get a nice look.
I hope it will help a little.
BTW: I'm not sure if I've translated tools names correctly. I use SW in different language.
first use "SPLINE" for curves of bottle
second for making outer curves use "FREEFORM" it's in "SURFACE"