My iphone SE thinks that there are headphones connected and as such I can’t hear my music or alarms – why?

It may be that there is a bit of debris stuck in the headphone port? If not then you could try these possible fixes, although if they don’t work then you may have to take it to your nearest Apple store is see if any of the geniuses there can fix it. If your iphone is quite old then it may be time for a trade.