Does anyone else have a difficult time saying, "No"?

Reading Boundaries has been a blessing.  It's caused me to think more about how

often I quickly accept an invitation to do something or how quickly I accept a new

commitment/responsibility.

Prov 31:16

16 She considers a [new] field before she buys or accepts it [expanding prudently and not courting neglect of her present duties by assuming other duties]; with her savings [of time and strength] she plants fruitful vines in her vineyard. [Song 8:12.] 
AMP

Today, I had to tell someone I can't watch their baby boy on Fridays anymore.  It

started out being every Friday.  Then I told them I wanted to change it to

Thursdays, but "they" wanted to keep him with me on Fridays - so they cut back to

an average of every other Friday, sometimes two in a roll, sometimes not.  Today, I

finally told them - I can't do it anymore and they need to make other arrangements. 

I just can't do it.  I feel maxed out.

The problem is I feel guilty, because I wish I could help.  In fact, I'm looking at the

situation and thinking - why can't I handle this.  It's not that often.  What's the deal? 

Fridays seem to get busy and when I have Benny (he's almost 1 year old) I have

to stop what I'm do for the whole day, unless he's napping or playing with my boys

in their room with the door locked (away from Angelena).  He comes at about 7 - 8AM and his mom picks him up at about 6 PM.  That's pretty much my whole

day.  The reason I have to stop what I'm doing is because my two year old

Angelena thinks he's a toy and wants to play with him.  She makes him cry and I

have to be on the look out all day long AND within reach - in case she's trying to

pick him up.  I've tried spanking her, but it's all day long.

Anyway, why do I feel like I need an excuse to say, "No."  I feel guilty just saying,

"I don't want to."  Am I being selfish?  These are the questions that people with

"Boundary" problems ask. 

When I was single, I had people's children all the time - for weekends, overnight, etc....  Now that I have my own, I feel like I'm just doing what I can to maintain

and do a good job with my family responsibilities.  Sometimes when I'm doing

better and I feel ahead of the game, I'll offer to help someone with their children -

but usually I'm doing all I can to keep up with my own. 

I can go and make a meal, clean house or something else for people, but watching

their kids is something I don't offer much of these days.  Why?  All I can think of is

I am maxed out with my own THREE.  Not even a large number, but it's all I can

handle right now. 

Alright, if any one has a thought, PLEASE SHARE.

thank - Vetta