Ex won't follow the parenting plan
We have it in writing that I get them every other weekend starting Friday after school. She's been keeping them through Monday 'just this once' three times in the last two months. When I bring it up she says I'm being rigid and the kids should come first. But I feel like she's changing our schedule whenever she feels like it. Do I need to go back to court over this or am I overreacting?
This is infuriating. You need to document everything - save those texts and emails about the Friday pickups she's missing. If she keeps doing this you might need to go back to the mediator or lawyer. Don't let it slide.
How long has she been doing this? Because if it's a pattern you might need to address it formally. I know it sucks but protecting your parenting time is important.