I agree with Tia on the "one more term" thing. and don't feel bad for thinking that... we ALL need "me" time.
As Tia says, set mini-goals, like the one more term thing. Just make sure u get a bit of "me" time everyday, I know how difficult this is with kids (I worked as a nanny for 4 years) but even if when the baby is having her nap, put a video on for the older ones for half an hour. and just relax, dont do dishes or tidy up their toys. Just sit down and read a book with a cuppa.
Give the older kids a drink of juice and a snack - I used to do a fruit snack bowl with a wee drop crisps and a few smarties - whilst they watch their video.
Even packing a snack and taking off to the park for the afternoon. I know you feel like "oh i cant be bothered to go out" But at least at the park, you can sit down and let the kids run wild, use up their energy and you can relax and know they are safe! And you do not have to tidy up after them!! 
Also, don't be scared to say to the HV if you are finding things too much. It's nothing to be ashamed of, and it certainly is not a bad thing against you. Parenting is bloody difficult!!
And of course, there's always us 
