I'm so sorry to hear about the nigtmarish naps (or rather lack thereof!). My dd went through the same thing. A couple of thoughts - it may be just developmental, which doesn't really help, except to say that it will get better. Here's a couple things I tried:
when I couldn't extend dd's naps with pat/shh, I'd try for 40 min, take a 10 min break (usually just rocking with her quietly) and try again (unless it was time for the next feed), then I'd feed her, and only keep her up for 30 min after she finished bfing, and then back to nap again.
I also started pu/pd at 3 mos, and dh had good success with that (I never could get it quite right). I did have some success with w2s - if you lo always wakes right at 45 min, try going in at 40 min and lightly jostling him (I'd tug her leg usually), that would work about half the time for me. the other times, I'd have to do pu/pd which usually meant no nap extension.
The biggest thing that helped me was having other bw moms to encourage me. Nap extension sucks, but it does get better. Abby is now almost 6 months, and her naps have gotten better and better. I'd say the worst of it was months 3-4. I know that seems like an eternity, but it really isn't. I'd just bring a book or something with me into her room while doing w2s, and if I got frustrated with pu/pd, I'd give myself a "time out" and take a break, then come back to it.
Looking back, I think it would have been easier if I wasn't so uptight about it, though I don't know how I would have stayed calm, since I think I actually did tear out my hair!!!!
Hang in there Bec.