I've had a lot of symptoms but I don't think i conceived when ovulating

I went to the doctor a week ago because i was having yellow diarrhea and some vomiting for about 2 weeks and he said while this was happening my contraceptive pill wasn't working and i'd had unprotected sex a few times during the time i was ill.  The next day i was due to come on my period and I'm never late and they're always the same, first 2 days im extremely heavy as in i always leak through and then it calms down for 2/3 days then brown for 2 days but this time i was 3 days late and since 3 days ago ive had the lightest bleeding which goes from very bright/light redy pink to a dark brown. I've felt nauseous and had a strong sort of sting in the back on my throat, my breasts are much bigger (as my partner has noticed lol) and I am peeing more than usual but im also very thirsty.. I've done a test before i started the bleeding and it was negative but i don't know if i took it too early and i can only afford the cheap ones.. 

any help would be amazing as well as any storys of what they were like the first few weeks!