YES, Yes, Yes! Anything you eat or take will be given to her through breast feeding also. It is definitely affecting her. You said you noticed it yourself as soon as you started taking it.
Babies can be more sensitive to certain foods too. You might take notice if she spits up more at certain breastfeeding times DEPENDING upon what you ate (if she spits up much). Sometimes dairy and certain vegetables will make them spit up or give them gas. Though, I'd deal with the zoloft issue first.
I did a little research. This is what I usually find: Antidepressants
Maternal depression is known to have an adverse effect on parenting and infant development.14 Tricyclic antidepressants have been shown to have LITTLE to no effect on the breast-feeding infant, although the AAP finds MOST tricyclic agents to be of possible concern.3,7 Taking a single daily dose at bedtime will limit the infant's exposure to the medication. The selective serotonin reuptake inhibitors (SSRIs) are generally the first choice of treatment for depression. Sertraline (Zoloft) is likely to be the safest choice among them because it has been studied extensively and because drug levels found in nursing infants are usually minimal.7,12
TABLE 1
Minimizing Potential Risk to Nursing Infants from Maternal Medications
General considerations
Avoid drug therapy when possible.
Use topical therapy when possible.
Medications that are safe for use directly in an infant of the nursing infant's age are generally safe for the breast-feeding mother.
Medications that are safe in pregnancy are not always safe in breast-feeding mothers.
Use reliable references for obtaining information on medications in breast milk.
Medication selection
Choose medications with the shortest half-life and highest protein-binding ability.
Choose medications that are well-studied in infants.
Choose medications with the poorest oral absorption.
Choose medications with the lowest lipid solubility.
Medication dosing
Administer single daily-dose medications just before the longest sleep interval for the infant, usually after the bed-time feeding.
Breast-feed infant immediately before medication dose when multiple daily doses are needed.
Hope this helps.
K.