Hi B
We have been to Caribbean 8 times now and have taken Chloroquine on all trips without any problems, but I do know that a few folks have reported that they make them vomit.
Your GP seems to be giving you stange advice as Malarone is not a normally recommended tablet for the caribbean.
Chloroquine is not recommended if you have epilepsy or psoriasis.
Proguanil ( or Paludrine ) is the other recommended anti-malarial for DR which can be taken if you have epilepsy or psoriasis.
Both the above can be bought cheaply over the counter at a pharmacy without prescription and need to be taken for a week before you go until 4 weeks after you are back.
Not sure why your GP would suggest Malarone unless you have an unusual medical condition.
For more information see :
http://www.traveldoctor.co.uk/namerica.htm#2nd
In my experience you will get the best advice from an independant pharmacy and talk to the Pharmacist ( who will most likely be the owner and so cares more about his business than an employee in a multiple ).
Good luck and stay healthy
Scubaman