How can you tell if ur pregnant while on birth control.?

I had to take antibiotics 3 times a day for 10 days while on birth control, and just a few days earlier I had skipped 1 day completely. On the third week of birth control, 5 days after startin my amoxicillin I had with bc as the only source of protection. Abt a 5 days later I began to feel dizzy, and nausea. Then my appetite increased. Also my dizziness came so bad that I nearly ped out. About another week later my period is here but it isn't right. Its a light flow, bright red with no clots, but its muscousy and watery. With light cramping, and all my other symptoms the nausea, dizziness, and hunger are still present.