I need to vent/need some advice

I'm 9 months pregnant and 3 weeks away from having my baby boy! We'll my friend who I haven't talked to in awhile asked me if I could watch her son last Sunday, sure no problem! So I watched him and it wasn't a big deal at all. Then Sunday night she asks me can I watch her step son and son on Tuesday so of course again sure no problem, later that day while I'm watching them she texts me asking if I can start watching her son once a week at this point I'm getting a little frustrated because I'm literally getting ready to have a baby and I keep doing all these favors and I have a problem saying no because she's my friend, so I said yes up until my due date and then I can't anymore. Then she texted me yesterday asking to watch both her son and step son Thursday and again I say yes but I'm really starting to get irritated then she texts me next day saying I don't have to come to her house but could I come to her step sons football game and watch her little son while were there I'm thinking WTF really. We'll forward to the football game I get there text her were is she and she tells me what? The games not until tomororw -.- I literally hit my breaking point and I'm like ok we'll I can't do it I have plans. I'm sick of running around doing all these favors! We'll then she texts me at 12:30 am and I literally want to lose my shit and havent replied but she asks do you think I could move in to your spare bedroom with you my husband and I aren't doing good and I don't have anywere else to go  Yadi yada... My spare bedroom is the nursery for the baby I live in a condo and she wants to bring her son and her in my home and I know why she works she is gonna want me to watch her son. How do I say no in the nicest way b4 I lose my mind!!