if any of us knew the answer mate we'd be fecking millionaires,it could be going light or it could be eggbound or it could just be moulting,if its going light then theres feck all you can do,if its eggbound put it in an hospital cage,in most cases heat alone enables the bird to pass the egg or get it to a vet,and if its moulting then it should be fine,but budgies do sometimes puff up when theyre relaxing so feck knows