Can caffeine cause nausea and migraines?

Nausea yes

It usually helps headaches 

Caffeine overdose can cause nausea, diarrhoea, light-headedness and urinary frequency. Caffeine withdrawal even after moderate chronic intake may be associated with headache, nausea, nervousness, reduced alertness and depressed mood.

It can definitely cause nausea. Caffeine is used to treat migraines, but if someone were sensitive to it I supposed it could trigger one if the person were susceptible to migraines.

Excess caffeine consumption can cause nausea and headaches.  Cut back on the coffee and it should ease up.

Bitter tea, fish oil, cucumber. Insya Allah help. Allahu akbar ! Viva Indonesia !

Yes.  And many other nasty side effects such as erectile dysfunction and uncontrollable flatulence.  

Caffeine withdrawal is a trigger for mine.

Caffeine withdrawal can.

The side effects of to much caffeine:

Restlessness and shakiness.

Insomnia.

Headaches.

Dizziness.

Rapid or abnormal heart rhythm.

Dehydration.

Anxiety.

Dependency, and the need to take more to get the same results.

Yes it is possible to overdose on caffeine