Ok, I'm really confused and irritated.

I have been on the same birth control for 5 months. 3 months ago my period was messed up (because thyroid medication) I had spotting. The next month it was back to normal. (So it should still be normal!) This month though. >_> the last 2 weeks I've been sick to my stomach everything, every single time I eat. I don't know what implantation bleeding looks like, but I'm not supposed to start my period for 3 days. I'm spotting what looks like watery pink highlighter (Suuupper thin watered down blood) for the last 3 days off and on. I took a pregnancy test this morning. Negative. Still nausea full blast, itchy growing child feeling in my uterus (I have a 3 year old I took the test 3 days after a missed period with her, negative, then 2 weeks later the next test said "surprise mom!!") I am 99% unsure how to deal with this. Never really expected this. (Also, married if I am it's no issue it's our little cupcake if I am) when do i wait to test again? Will the birth control hurt my possible little cupcake? O.o I knew antibiotics messed with bc, never expected thyroid medicine to mess with it this much. Someone please help, any advice is appreciated!