It is that time year again where everything starts coming to life except the bacteria that balances the ponds natural equilbrium(low water temperature does not help). I agree with ratbag66, maybe there is is a peak in your ammonia/nitrate levels. Get yourself a test kit to check the levels. If they are high I suggest water changes(de-chlorinated water only) to reduce the high levels. Although Goldfish are very tough creatures they do need some tender loving care. Look at their dorsal fins. If they are erect then they things are not too bad but if their fins are clamped to their bodies, carry out water changes ASAP as things are not right.