Help needed to best help a possible sick bird

[Wargie]

Help please, I have two male finches for a year now. One zebra finch and one society finch. My society finch is acting quieter then normal . he is eating and drinking, but is really puffy and when he breaths his tail bobbed as he often had his beak slightly open. The eyes and nostrails are clear and clean .

We are having strange weather, cold in 20 to 30s, (at night. And early morning) then back to 50 snd 60s (during the day and lots of rain) I put a heat lamp by his cage to help him maintain his body temperature. Is their anything else I should do or advice. As taking a bird to the vet is very expansive.

Thank you
Wargie

[Wargie]

So update my bird has been under a heat lamp and he is less fluffy and more active . the tail bobbing has stopped , adding a probiatic to the water.