With the description you've given, this sounds like a tape worm... and the best med to use for that would be PraziPro. Before
using this medication I first would have to ask what kind of filter you are running on this tank? Is there carbon in it? Is the filter you are using rated for the tank size you have?
During medication you will need to remove any carbon that is in the filter. Take a look at your tank, is the output of water flush with the surface of the water or is there space where the water "falls" into the tank, breaking the surface of the water?
I also suspect the bubbles are from the water conditioner, and the easy was to tell and to fix it would be to do a few water changes without the conditioner, and make sure there's a lot of carbon in the filter when you do this. (This means you can only treat one issue at a time, and I would do the medicating first considering the condition of the betta)
The other thing I would highly suggest would be to test the pH in your water supply (tap water with no conditioner) and then test the water in the tank for pH again. If they don't match exactly, post the results here and we can help you. Too much water conditioner in the water can cause pH to drop over time. If this has begun happening, then water changes need to be done much more often and much less water at a time to avoid shocking the fish...
If you have more questions, please post before
making changes or medicating. Depending on what type and size of filter you are using, you may need to run a few air stones in the tank during medicating. I won't know if this is needed until I know what kind of filter is on the tank. I can also help you find the med online if you need, just let me know.
One last important
note: PraziPro doesn't mix with all medications, so to avoid turning your tank conditions toxic quickly, please make sure you do at least 1 - 2 water changes and run carbon in your filter for at least 48 hrs before attempting to use the PraziPro.
Hope this helps...