Can I take alka-seltzer while breastfeedin?

Maybe,maybe not. There are at least a dozen products carrying this name and some contain antihistamines or phenylephrine that can decrease milk volume, or Aspirin that should not be consumed iy baby may get a viral illness while you are taking it. So some products without the ingredients noted are less worrisome than others. See:hale, t "medications and mothers milk", 2012 ed.
Ask the baby. In all seriousness should not be an issue for you or baby.

Related Questions

Can I take alka seltzer while breastfeeding?

Depends. This is a group of products rather than one.Most are considered ok if the baby is healthy but the Aspirin containing forms should be avoided if baby has a virus. Read more...