I plan stories out but then my brain decides it's going to go straight on to planning the next story, like its thinking the story is finished so onto the next one, time and time again it does this, is it possible to persuade my brain to work on the story I just planned, instead of going straight onto the next story plan?

I wonder if you're planning in too much detail?  You may be leaving your brain with nothing interesting to work on, since all the essentials have already been set down in the synopsis.  Try writing an outline, nothing more, and letting yourself work out the details as you go.

Good luck.

its kind of an alternative history thing, don't know if the idea is even workable

Basically its set in Henry the 8th's time, the Queen he had a son with, the baby son dies shortly after birth when the Queen and the baby son are left together, her lady in waiting also had a baby and because she was sure King Henry the 8th would execute the Queen over the baby dying, she swaps her baby son with the baby who died, to save the Queen from going the same way as several other of his wives, in this alternative historical storyline instead of divorcing any of his wives he has them executed for not producing sons

The story plot that I wrote has more detail than this, just stuck as to how to start it without getting caught up in the details of what I already wrote down

(I expect someone will probably use this idea, I'm not great with alternative history so it might end up in the unworkable ideas pile that I end up abandoning)

if it does, I'm happy someone taking this (someone probably already has thought of the whole "what if the son Henry the 8th had survived" thing)

(I expect someone will probably use this idea, I'm not great with alternative history so it might end up in the unworkable ideas pile that I end up abandoning)

if it does, I'm happy someone taking this (someone probably already has thought of the whole "what if the son Henry the 8th had survived" thing)

This bit above suggests to me that you've already told yourself this idea won't fly.  Well, not for you.  Not at this time.

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If you can't truly believe in it yourself, then you won't really want to make the effort of finishing it.

Too much detailed planning/plotting can become a barrier to creativity, because your mind will be trying to slot the previously written details into place amongst the newer workings of your mind, and quite often they won't mesh nicely.  Like two jigsaw puzzles cut out in the same pattern but with different pictures.

I'll tell you a little secret though.  Quite often the start of the printed book is nothing like what you expected to be the start when you started writing.

This is because new writers often have a few paragraphs, sometime a whole chapter, of 'getting into their stride' before the real storytelling takes over.  Before things start to flow.

Here's a thought.  Start partway through what you already consider to be the real story.

Maybe kick off with the lady in waiting watching the young prince, let's say as a lively infant of five years or so, and feeling rather proud of how he's turned out but knowing she can never tell anyone the true story.

Stories rely on conflict, and the conflict in her own head will be enough to get you thinking.

Next possibility?  The Queen doesn't know. If the babies were swapped whilst she was still spaced out on Laudanum or some other historical pain relief this is quite plausible.  (Even now, with tagging and all the paperwork, babies sometimes get accidentally swapped and taken home from hospital by the wrong family.)

In which case possibly the only other witness would be the midwife.

To add a twist the lady in waiting, whose baby had ostensibly died, could have been given the role of wet-nurse to the baby.  She would have fed it regularly, with all the motherly feeling this triggers, but never been able to tell.

There's an emotional snake-pit there to play with  ;-)

Always ask yourself the 'what if?' questions, and don't automatically adopt the first answers that pop into your head.

Life is inherently messy, and the lives of your characters should reflect this.  Make them earn their triumphs, and stagger from their disasters.

If any of this helps, you're welcome.  If it doesn't I won't be offended.  It's your story, not mine.

Gyppo

This is wonderful advice for writers, Gyppo. I always try to remember to arrive late and leave early with my stories. It's right up there with kill your darlings.