sounds to me like she is looking for attention, how recent is the divorce? and how well do the two of you get along? is this third baby his or is she dealing with a new man in mommy's life as well? all of these things can cause a child to act out to seek attention or to regress to behavior that is suited to a smaller child in order to get that attention, and like you said you are tired of consistently being a grump which means she is gettting a LOT of attention doing these things so in her world it is working and she will continue to do them, i don't think disipline is the answer so much as finiding a way for her to get positive attention for things you like for her to do in order to break the cycle, and as a single mom that is hard to do not to mention the fact that they aren't there all the time. you could try changing the shared paernting schedual a little bit to grant you some alone time with her and with your son as well, say you drop him off at 3 and her at 6 and have dinner or play with just her for 3 hours and then you pick him up at 3 the day they come home and do the same thing. something else to keep in mind is that if this is attention it will get worse before it gets better, with a baby on the way she is due to lose even more mommy time than she already has, so try to find the good things she does and even if it is silly or seems to be no big deal to you make it a big deal, make it as big a deal as the stuff she is doing wrong and break this negative attntion cycle. good luck.