Ive been at my job for just over a month an have been hospitalised twice. Once for 2 days and the second for 2 days. I followed protocol by informing my manager and such. But I have hear rumours they may sack me. Are they allowed to fire me? Please help!

Yes. First of all you are still in your 90 day probation period. Secondly, if you are in a work - at - will location, they can fire you for any reason they choose.