how long have you been off for?
maybe they think its too long for tonsilitis?
or maybe they think you have come back too soon and are spreading round germs risking making them all ill..
if you are coughing sneezing and spluttering all day i daresay its just a bit irritating - especially if they sense you are putting it on a bit ...so, are you?
you clearly want them to believe you have been very ill and have some sympathy for you... have you perhaps been 'demonstrating' it a bit much...?
i wouldnt blame you if you had to be honest... you want them to understand you truly have been unwell and still are - but a fake, forced cough is very easy to spot...and wont go down well...
i get quiet annoyed when people come to work - or even the pub - when they are utterly riddled with germs - they think they are being brave and soldiering on - but really they are just spreading it round - and to people who are vulnerable - old, young, asthmatics etc it becomes a lot more serious than a bit of a sniffle
also tonsilitis does not 'turn into flu' - flu is a virus and tonsilitis is bacterial - so not connected ... so if you are going around telling them that they probably think you are making up illnesses and playing on it ...
i do think you are being paranoid though ... a 'feel' in the office could just be in your head...if you think something - you will see it everywhere - and thinking they are emailing each other about you - how could you possibly know that?