Blueberry bush Q

Can any of you tell me....should I cut back a blueberry bush at the end of each fruit season?
I've had one for a few years and it had always been generous with berries but this year it's poor. I wonder if it's because I've never cut it back?

 

Ok I've watched some YouTube videos about pruning. They say to cut back the thickest/oldest stalk but if I do that, it's the main bit of the plant?!

Ps. Does it need a bigger pot perhaps?

 

I have four Blueberry plants in my allotment from which I normally get good results I also had two in pots in the garden and hardly ever got any fruit so moved them up to the allotment with the other plants and now they produce the same as the rest do I think they are better in the ground if you have any spare garden patch

 

I think it needs more compost in as after watching youtube, I can see that the root ball is exposed.

The only garden area I have floods constantly, and even when it's been warm and dry for a period of time, the ground is still very wet and boggy.

When would it be advisable to transplant if I can find a bigger pot? In real life the pot is actually quite big, the photos make it look tiny.... I posted the pics then edited to ask about pot size and then went out to garden to see it, but it is bigger looking in reality!

I don't fertilise it so I'll def try that too. I'm so unsure about how/where to prune it though