Pain in the knee…

This is a bit of a story hope you can stick with me and maybe offer advice & opinions.
So been running for 20 years no problems running. Running 21 miles average per week for years and years.

Over 2016 I achieved a few PBs 10k - 50 mins , 4miles - 30 mins and 3 miles 23 mins.

Also increase my ability to maintain a fast 3-4 miles then drop speed to accomplish 7 miles in under an hour.

Things were going swimmingly so it seems for years and years running in over-pronating Saucony trainers buying the same model for over 6 years. Before that I had Asics OP moderate trainers.

12th December, 2 miles into a 5 mile run my knee felt as though it collapsed with a shooting pain towards to back of the knee cap so much so that I had to hop to come to a stop could not put my leg back down. After a minute or so was able to continue moving by walking & skipping no pain whatsoever but again as I started to run the shooting crippling pain  returned to stopped me mid-stride.

I run on the balls of my feet.

The only way I could continue to run was to lower my stanch so I have bended knees and run heel to toe slowly - and i mean real slow. 1 mile = 11 minutes!!!!

I was still able to walk, spin, tuck jump, squat, burpee, step up, high knees but as soon as I run (treadmill or road) shooting pain within 10 mins or so.

I then booked a doctors appointment in January to see if I could be referred for an X-ray - I was thinking loose cartilage after reading up, but GP laughed as he swung my leg around bending it here and there as I said "nope no pain, and yes I still can do other exercises" . He said NHS is stretched and "won't refer as you can still do other things just REST the running its only been 5 weeks…" oh "you could pay £200 for private scan/xray" - like where am I going to find that cash?

So left frustrated I love out doors running I can't bare to think its all over for me at 40 years old.

Went for a slloooooowwwwww run 4 miles took me over 40 minutes and I ran it crouching down running in a weird heel flat foot slapping mode to make the distance with NO PAIN. Passing a running shop on the way back I stopped off and spoke to the sales assistant telling her all this and she said "lets film you running on the treadmill". 

Video showed me overpronating even though I was wearing my Saucony over pronators. She then looked at my trainers and said " you have neutrals on" I was insistent that I didn't - I know trainers and I know I need OP moderate and that I'd been buying these type for years… she sweetly pointed out I had Saucony Rides and what I needed were Saucony GUIDES!

To cut this bit shorter - yes she was right - somewhere on buying my trainers I'd gone wrong and thought I had OP but brought the wrong type. I assume that over time the 'GU' had worn off a pair of Guides to leave 'IDE' and when I'd purchase more online I thought they must be Rides not Guides.

So two years at least, (I know this time period cos I've had new pair of the same model/colour etc 2015 & 2016 I always buy a new pair around January) of pushing myself in neutrals only to finally fall apart at the knee.

Well with the new Guides I'm slowly building up again my miles - currently can do a 5 miles with no pain hitting heel to toe on the left (bad knee side) and ball of the foot on the right. As soon as I try to run ball of foot on the left I get the shooting pain again. I'm not as fast as I was either by a long shot.

1. worried I'm pushing it too fast and it will collapse again and I'm just glad to be outside running again  
2. still feel a weakness there (I think so? is it mental? I dunno?)

My questions are
why still the pain if I don't hit heel to toe - have I done an large injury that is still healing
will I ever run fast and my normal running poise again
who can tell me as a doctor thinks I'm nuts

Currently running a mile in 8.30
Used to run a mile in 7.30

Thanks for reading any helping suggestions welcome