Genuinely Poorly And Scared Of Losing My Job, What Shall I Do?

I recently started work about 3 weeks ago in a job I love, strangely enough. But yesterday I suffered from diarrhoea and couldn’t get in to work (I rely on a long journey bus service) as I needed the toilet too bad. Now I rang my boss/owner of the company and I said that I would be an hour late for work and I told him exactly why, and he was fine with it. Now I got ever so near to work and I needed the toilet, this time it was really bad. So I rang him again and said I don’t know what to do. He then told me to go home to bed and said he was a good judge of character and that I wouldn’t mess them about. Which I am swear I am not doing. I then went home and took some diarrhoea relief tablets and they worked, worked almost too good infact.
I then went to sleep with the view of going to work the next day (today) but when I woke I felt awful, worse than before by a country mile. I am extremely lethargic, bad stomach pains, a cracking head ache and I am now constipated (believe that if you will!) I tried to go to work, but I couldn’t make to the bus stop never mind to work. I rang my boss, and I said, I feel worse than yesterday and I can’t make it in. He didn’t seem to pleased on the phone, he was very dismissive about the subject. I said on the phone that I will be going to the doctor’s today and his reply was “alright” and then the conversation abruptly ended. Now I did go the doctors, and I am indeed really ill. I said to the doctor that I need some sort of proof about this as I fear my work think I’m taking the piss basically and I do not want to lose my job by any means. She refused and said I have to be off for a minimum of a week for a sick note. She then proceeded to say that I must not go in to work tomorrow as I risk spreading my virus, she did say however that she would be more than happy to answer a phone call from my work in the event of work not believing me.
Now, I am scared about ringing in tomorrow and saying that I will be off for a third day running. I don’t want to lose my job, as it is something I enjoy doing and got very lucky to get it in the first place.
What shall I do? Shall I risk going in, and maybe passing out or pooing myself? Or shall I ring work and tell them to ring my doctors as proof about my illness?
I am 21, living alone, away from parents, and I’m scared of losing everything. I apologise for this rather large rant.
I will appreciate all answers that come my way.
Thank you