Even with a baby, it is still possible, but don't be scared to slow down if you need to. You should not have to feel lonely (though I completely understand - I shed lots of tears over the same thing!) and I think that Chippy's idea is grand. Have an official break from it. I defended my PhD last year, having worked and studied full time - I didn't have the toddler to juggle aswell but I did decide part way through that my life was so boring that a 2 year contract in China was just what I needed to spice things up. My uni agreed to giving me a year 'off' as I thought that moving countries and learning Chinese on top of work and PhD study would have pushed me over the edge. I had 6 months of that year doing next to no PhD work and it gave me the time to gather my thoughts...plus an extra six months to work unofficially on my PhD. So on paper I submitted in 3years and 1 month and I now I'm back in the UK, with my PhD in maths, a couploe of years work experince from an amazing country and I can speak mandarin. I wonder if a year off for personal reasons, which you can use working every other weekend on your PhD to keep the rhythm, could work for you too. Don't lose hope though and don't give up...you can and will get there and it really is worth it :-)