What Is The Reason For Me Having Repeated Illnesses ?

Just after xmas i came down with flu i was prescribed tamiflu as im asthmatic i got over this then 2 i am 32 female with asthma which is controlled by medication, i have had my yearly flu jab. Afew days after xmas i became verry ill, i was prescribed tamiflu and antibiotics for infected synusis. I recovered wees, then 3 weeks later became verry unwell again so i had tamiflu again with prednisolone 5mg six tabs every am and more antibiotics as had very bad chest infection, i again recoverd only to have to go back to gp with pain in right ear and right side of throat he told my to get sudofed as have fluid in ear cannal pushing on my eardum? The sudofed have not helped despite taking paracetamol, last night the awful body aching started with continuous headache and vomiting with a fever . I saw dr today who seemed puzzled urine nad, temp ok chest slight wheezing, advised to see gp tomrw for blood tests, however if i get worse than i am currently im to go to a and e for blood tests and chest xray?? why do i seem to be so ill for so long? what can i do to help my immune system and what could possibly be wrong with me? Any advice is greatfully received.