TTC our 2nd child

Victoria • 💗Mommy of 4 angels👼👼👼 and one little boy named Viktor and a little girl natalia! Pregnant with #3

So I had my baby almost a year ago and I breast fed for 9 months, still haven't got AF not even spotting and we have sex a lot! We've been trying TTC for 6 months now and every month around the same time I get pregnancy symptoms but a negative test! what is happening!?