my dog became fearfull

Hi!
I don't even know where to begin:sad:
I got Bilbo last February. I was told that he used to live with big dog and two cats and was fine with them.
Very soon after we got him he undergo surgery and we had to follow recovery period when he was not allowed to walk more that 5 minutes 2 times a day on a leash for 2 months and then longer walks on a leash for another two months. No dog parks, no play with other dogs.
Of course we met other dogs in the park and he was very interested in them, looked very friendly especially with smaller dogs. So I was waiting for the final x-ray to be allowed to go to the dog park.
When it happened and we went to dog park there were two dogs medium size and Bilbo played very well with one of them. Second time there were many big dogs and Bilbo didn't want to live my side:confused: with tail between his legs, so we left:sad:
I started notice that he doesn't really want to say hi to a big dog anymore.
But this week he is even more scared. Even with people that he met before:confused: I'm not sure, but I think it got worse after his first obedience class last monday. He was not really happy during the class and was scared of another dog there (it was pit bull, dominant, but not aggressive).
I don't know what to do.
Should I try to continue obedience class? Should I walk him to dog park?
Any suggestions?
Bilbo is 3 years old basset hound.

Thanks.

I would start with meeting one dog that you know already and letting them "socialize" a few times and see how that goes before introducing him to a few or strange dogs he doesn't know.

Prin, thanks for advise! So , better not dog park for now?
Is it possible that he became not socialized in so short period of time?
What should I do about his class? Cancel it for now? or maybe ask to change the group? Now there is a group of two?

If he had one scary incident, yes.

Better stay away from the dog park for now. He needs to regain his confidence first.

Can you stay in the lessons but keep the other dog far from yours? If not, change groups.:shrug:

I will give the second try to the class. If he will not enjoy it - I will stop it. At least for now.
I didn't really noticed any scared incident with Bilbo:confused:
Just one dog barked on him, but was not even too close, about 10 meters away.

since he is 3 years and has had no real trauma with another dog, I am going to suggest it may be medically related such as hypothyroidism