The swollen belly may be from parasites.
I had a young CT - F with a swollen belly and cranky attitude. Went through all of the above trying to unconstipate him... she pooped alot, but still continued to swell.
I got some anti - parasite food - and the belly has gone way down. Another couple weeks of treatment are left (three contiguous days anti-parasite food for 6 weeks). She doesn't like the food much (I do crush it, so it is bite sized for her), but over three days, she eats some.
Her attitude has majorly changed - she used to be so mean, attacking the other girls - and eats less (she used to eat everything in sight). Thank goodness I figured out what was wrong!
There are other reasons for bloat - like bacterial infections, for instance. Just wanted you to know what happened in our situation.
Good luck to you and your betta! Hope your buddy feels better soon. :)