Therapeutic Dose and Meds Losing Effectiveness

Hi,

I’ve had to increase my ssri dose three times in a year. I had a great response to this med, but seems to lose effectiveness fast. I’m not bipolar. I also had huge hormonal changes due to pregnancy. Has anyone had any experiences with their meds losing effect often? Does anyone know if this could be due to not reaching your therapeutic dose? Also, how do you know when your therapeutic dose is reached?

I’m in the middle of an increase and really looking for some encouragement-thanks a lot!