When dealing with a headache, try boiling one cup of apple cider vinegar and one cup of water in a pot. Pour into a heat proof bowl and put on the table or other safe place that you can lean over the bowl and cover your head with a towel. Inhale the steam for a few minutes to bring some relief.
The warning on mine says not to use prior to 4 months of age. My son was in his Jolly Jumper from 3 months. The directions of use are that if they can confidently hold up their head then they are fine.
What do you mean by bouncer? The vibrating chair they can go into anytime, but baby may not like it. If by bouncer you mean Jumperoo (attaches over the door frame and baby uses legs to jump & bounce) then the baby should be able to hold up their head- around 3-4 months. It's never a good idea to leave the baby unattended in the bouncer.