Hi, I've been having the same panic so I've been to my teacher and got this really good advice... to get into the higher grades you need to be writing with more of a thematic approach instead of just addressing one source at a time.
So instead of analysing the content then the provenance etc of Source A then going onto a next paragraph and doing the same with Source B etc you need to pick a point to write about. Ok so the easiest way to do this is in your introduction set out the groups of sources which you will be addressing - in your planning time you need to decide which sources agree/disagree - usually there will be 2 for each and one in the middle - you need to set up this argument in your intro. Then you can go on to write about agreeing or disagreeing as your 'theme' or if youre more confident its better to pick something which obviously is coming up in the sources - AS LONG AS IT RELATES TO THE QUESTION! You then need to address these themes, either agree/disagree or other and assess how the sources support what you're saying.
So find a common point/theme, use evidence from the sources which all back up what youre saying, and you must use your own knowledge as well to support your point. Throughout this you need to be also assessing the provenance of the sources to judge whether what they say is reliable/useful and then come to a conclusion overall about whether the sources agree or disagree with the interpretation.
It will not always be the quantity of sources that agree with the interpretation but it is the quality - if there are loads of unreliable sources saying one thing but a couple of reliable saying another - go with the couple!! You need to set out your argument in your intro and sustain it without your essay then reiterate it at the end.
The main thing to remember is to keep focused on the question and always relate your points back to if this shows the sources support the interpretation or not. I'm not sure if I've explained it properly but i hope this helps!!