everything's fine it's just normal and they are right.
Is it normal, though? Because I can see several things in your quite brief post that aren't normal to all happen at once!
- Colleague sickness leaving you to cover work over and above your pay grade, which I assume is more high-stakes than your everyday duties
- Working over your contracted full time hours on the regular
- Studying for a qualification
- Revising for exams
- Parenting a toddler
- Parenting a man-child
Any ONE of those on top of your normal job would put extra on your plate.
This lot combined is not just a lot on your plate, it's a bloody all-you-can eat buffet of stress!!
It is now at the point where you are having dark thoughts and that is NOT sustainable. Anyone telling you to just suck it up and get on with it can be firmly told to get to fuck.
First of all, can anything be arranged at work to take some of the pressure off? Studying/revising whilst also covering not just one but TWO managers is doomed to fail. I would be going to someone at work (whoever you're currently reporting to in the absence of your own manager) and asking for some changes to be made. Off the top of my head, I'd suggest asking if the qualification could be postponed to a later date once the managers you're covering are back at work. OR, that you continue studying, but someone else takes the lion's share of the cover duties/time. OR, you get allocated X hours per week in your schedule where you go away from everyone else somewhere and study, uninterrupted, for that time.
Then to sort the home life. Your DP needs to get off his arse and cover you, while you are trying to better yourself at work for the benefit of the whole family. If he sees your relationship as teamwork (which it should be) then he should be eager to step up and do extra during this time. Because ultimately he, and his child, will be reaping the benefits further down the line.
I know it's frustrating to have to allocate work to him and explain how to do the most basic of tasks, but if you don't do it now, he's going to remain a net negative on the household forever. He MUST step up now, and let's be honest, he should WANT to if he values and loves you and doesn't want to see you struggling.
If he's happy to sit on his arse while you run around doing everything, well - that's not a man I could respect, or would want to be with.
Please try to carve out some time for yourself this week to just sit and be. No demands, no phone calls, no toddler tantrums, no "but what shall I do with this bag of rubbish? Put it where? Oh, does it go in the bin? Shall I put it in there, then? Well you have to tell me these things or I won't know!" (as you can probably tell.... been there, done that!)
Try to offload some stuff as a priority, but if you continue to feel so overwhelmed, please speak to your GP. A course of ADs during this very trying time is not a bad thing. 