Good news if you are breastfeeding and exhausted...
On caffeine & breastfeeding - some factoids...
Very little of the caffeine in coffee actually makes it into breastmilk.
Caffeine appears in breastmilk within 15 minutes of consumption by the mother.
Caffeine reaches maximum concentration in breastmilk within 1 hour.
Only approximately 1% of the caffeine a mother ingests makes it to her breastmilk.
Some babies, especially those with medical conditions or those under 6 months of age, may be more likely to react to this small amount.
Babies who seem irritable, fussy or wakeful may be affected by caffeine intake. They may also have a harder time staying asleep (Mohrbacher 2010).
CONCLUSION: if a breastfeeding mother has a moderate intake of caffeine (2 to 3 cups daily), there's almost no chance that it will affect her breastfed baby.
So have that latte. You probably need it.
SIDENOTE: No one should be commenting on your choice to drink caffeine, whether you are pregnant or breastfeeding. Your body, your baby, your choice. Though these people think they're being helpful, it's none of their business, and they are clearly ignorant of the facts, so feel free to educate them.
Link to a comprehensive article on this topic from La Leche League International, with references:
https://www.llli.org/breastfeeding-info/caffeine/