So sorry to read you have been feeling so rubbish for so long and that you don't feel doctors have been able to help you. And that you don't feel 'heard'.
Nobody hear can diagnose you.
And yes, there are loads of things that current medical knowledge and tests cannot figure out.
You are not saying what tests you've had, but it is entirely possible (and you are not alone in that. At all) to have lots and lots of 'normal' tests and still feel terrible.
I loathe and detest the phrase 'all in my head' btw - no dr worth their salt will ever say or think that. Mind and body are very closely linked and whatever one feels will affect the other. Nobody says to somebody who is depressed due to chronic pain "you should be happy, it's all just in the body", do they?
There are screeds and screeds of publications and people far cleverer than me are doing research on 'medically unexplained symptoms' - I can only begin to imagine how frustrating it must be to have something distressing that nobody is able to pin down. Sometimes (and I am in no way saying that you are at that point) a decision needs to be made to stop chasing 'an answer' (some things just don't have an answer) or even a firm diagnosis, and start managing how you are feeling and functioning; prioritising things.
Many problems are not structural, but functional i.e. how your swallowing muscle work, not what your throat/gullet looks like.
For instance re swallowing problems: if you have had an endoscopy then it will have been established whether there is a structural blockage or other impediment to your swallowing. If there isn't, there's little to be gained by looking again IYSWIM.
Do you trust your doctor?
If not, can you see somebody else? Sometime a fresh set of eyes is helpful.
Believe it or not, from a medical point of view, something going on for a long time without tests revealing anything is a reassuring thing. Bad things tend to progress and come to some kind of ugly head.
My advice would be to have a good long conversation looking at your symptoms, what was done to look at possible causes and then address how to manage them.
Whether or not this is all 'in your head' i.e. caused by stress/anxiety/major life event of having a baby/a combination of those factors and who-knows-what-else or turns out to be some weird and wonderful physical thing that has not been figured out yet, ultimately what matters is How You Feel. So start addressing that: if you need to take your Omeprazole daily or need to increase your dose, discuss that with your dr. If the whole thing is getting you down, seek some help with that: anxiety/stress management can make a huge change to how we feel physically. If going out stresses you out, then set goals: "Today I'll make it to my back step" "tomorrow I'll go down the lane" "the day after that I'll go to the post box". Or something like that 
Accepting that there might not be 'an answer' is NOT akin to giving up, but can give a whole new perspective in trying to tackle how you are feeling.
Sorry for the novel.
I hope some of it helps a little.
Speak to your dr, write questions down, write their answers down, go back if you need to and understand why what is happening.
