Hi Zulu
I feel your pain dear. I'm sure you are one of those ppl who, like a lot of us here, have that over exaggerated sense of responsibility almost to the point of being a martyr! Problem is, all the while that you are doing what you "should" do (according to your very thick rule book of what a mother & wife/fiance/girlfriend ought to do for her family), YOU are not feeling good/happy/fulfilled inside...then you feel guilty cos SURELY, you should be happy doing what a "good" mother/wife/fiance/girlfriend should do...
Well, it doesn't quite work that way. Save for a VERY few select group of ppl which includes Mother Theresa and the like

, most of us need to take care of "ME" in order to really be happy taking care of others...
When I start to feel claustrophobic and have that "trapped" feeling or start to feel overwhelmed, I have learnt to put tools down!If the nanny is away, I leave the baby with my husband & get out of the house! Even if for an hour. Go to the mall, buy a book, window shop, have a coffee/lunch all by myself etc.
With respect to gym, I do that weekdays and I leave home at 06:45 to make the 6am class at gym. I try to get to work earlier, around 7 - 7:30am and skip the lunch hour thing so that i can get home early. That way, even tho, I left my baby still asleep, I get to spend an extra hour or 2 with her in the evenings.If u can't do the morning, why don't you pack your gym stuff &go to the gym straight from work? Going home 1st then leaving again for the gym would challenge even the most avid gym-goer.
With hair and nails and all, make the time. so maybe one Saturday a month it becomes non-negotiable that it is mommy's "ME TIME."
I also sometimes (always) feel guilty about spending money on myself, but again, I know that I am aperson who likes to have hair and nails done and new clothes every now and then & I know how UGLY I feel if I have nothing to wear in the morning, or my hair looks crappy. & feeling that way doesn't do my family any justice so rather work out a way for everyone to get a treat once in a while. What I like to do is to have a month where I know its all about Baby and I buy her whatever I think she needs (& spoil her a little

) then maybe the next month, I don't spend (except on essentials like groceries obviously) then the next month, it's about me then DH etc.
Taking care of you is part of taking care of them.