I had this last year after taking on a lot of new training that would keep me up till midnight every night of the week.
What worked for me was this:
First make a list of every single thing you need to do, (I used to put it in 4 parts; home, class, training, planning.
Next, cross everything you have already done.
Then, cross off everything that doesn't matter (trust me, there will be loads).
Then write down everything that does matter but isn't needed to be done urgently, on the next page (this is the start of next weeks list). Cross these things off of the list.
You will be left with a very small list of things that have to be done and can't be avoided (for me this was usually planning, marking, assessment).
Now, your workload is greatly reduced. (do this weekly, I keep my list updated throughout the week and then spend 2 minutes crossing stuff off once a week at the start of PPA time, and I have been known to add things to the list that I have done, just so I can feel better about crossing them off. Cross them out using a highlighter, that makes it look like loads done too!)
Now that your workload is greatly reduced it is easier to target help. Let's assume you just have planning and marking on the list. Ask someone from SLT who the best person at marking in the school is. Then take three books to that person and ask for some help.
Do the same with marking.
By reducing your list, you can easily pinpoint who is the best person to talk to about each element that you are struggling with.
And please don't think for one second that you are the only one who feels they are struggling, everyone will be feeling the same.