Stretched too thin

I feel like I'm about ready to snap and that's scary... I don't like getting angry it scares me. I was angry for years and I'm so afraid I'll go down that road again. I just feel stretched so thin I don't know which way to turn, who to say yes to and who to say no to. Tonight for example I worked a little late...had my 8 hrs in at 4:30 but stayed till 5:10 to finish up some things cause I won't be working tomorrow morning. Got home after 6 and already knew I had to take daughter to the store for baby stuff (formula, bottle liners etc.), go to my mom's to fix her computer and try to squeeze in a visit with dad. All this in one evening because I am leaving after work tomorrow (thursday) to spend the weekend with my boyfriend and get a break from this crazy world I'm living in. Well I grabbed a sandwich while I was home and took an hour going to the store. Visiting hours are over at 8 and it was already 7:25 so I called mom... she was at the hospital and I told her I couldn't make it tonight but I'll go tomorrow as soon as visiting hours start at 11. When she was leaving the hospital at 8 she called me and I met her at her place. Another hour fixing her computer then my sister showed up so I couldn't leave right away. Finally got out of there at 9:40. I cried all the way home I was just so overwhelmed.  I don't know why I feel like I have to do everything for everybody. The thing is I'm the only one in the family that knows anything about computers and I know my mom can't afford to take it in for some simple thing I could do. My daughter, well she's my responsibility. I have her, her boyfriend and the baby and no one else in the world seems to give a damn about how they survive except me. I don't want that responsibility but who else is going to do it. They don't have the means to support themselves yet. And visiting dad well that's just something a daughter should do... I don't visit as often as my two sisters but I really would visit less if I didn't feel so guilty for not going. How do I get out of this trap I've built myself? How do I do less without feeling so guilty? I just don't know and the thought of it causes me great anxiety.  And I don't even have any support or understanding from anyone in this arena. If I mention my daughter and the financial strain I just get anger from my sisters and they tell me to order them to get out and get jobs... I have done this and they are trying. My sisters don't even think I should ever drive them anywhere.. 'make them walk' they say. The baby has alot of appointments and I want to be involved.. he's had health issues and I told my daughter I would be there for her and the baby so I end up working from home and/or taking hours off work almost every week for some appointment. But dealing with doctors and specialists is alot for any mother and she's only 17. Even my boyfriend gets upset with me for taking the time from work to take them to their appointments. I'm so overwhelmed I just don't know what to do. I don't want all the responsibility; I want my daughter and her boyfriend to be more independent but its not going to happen overnight. I have enough stress just trying to do the right thing and then I have to deal with the backlash from those who think I'm doing too much. I want to go away - far enough that no one will call me to help. I just feel like running away... i can completely understand these people who stage their own disappearance and start over somewhere else. I couldn't do that to my family but I can understand how someone could.