My son is now 11 weeks old and I have had enough he can't seem to keep anything down his reflux is really bad should I change formula he is growning so he not under feed but I try to feed him every4 hours just 200 mills but will not finish then bring half up again in a matter of minutes

I don't think we have any Pediatricians here so you will get better/safer advice by calling your's .

Usually if he is gaining weight and not showing signs of distress, such as pain, it is more of a matter of inconvenience than medical concern. Have you spoken to his doctor about it? Best to let them guide you with any formula changes if necessary.
Some babies will need a switch and, on occasion, medication, but usually medication is best used only if they are not gaining as they should be.
Many babies will have reflux and they usually outgrow it after several months.
A few things you might try if you haven't already... smaller feeds more frequently... have him sit up for about 20 minutes after a feed before lying him down... stop a feed after a couple of ounces, break, and resume for another couple of ounces, etc..