I'm sorry no one has answered your question.
If you haven't tried those three meds, you have not tried everything. Topomax especially is a very commonly tried medicine. Its usually second or third on the list. I hated the stuff. It produced extreme problems with short term memory. I'm a little rare in that my reaction was strong and came on with the first dose. Usually, its not a problem until you get to the higher doses. A lot of people can't stay on it because of the side effects, but you might get lucky with it. Maybe about 25% of the people who use it LOVE the stuff. It has the potential to completely relieve your headache problem.
Effexor is an anti-depressant. It has a stimulant effect at first, but you'll get over that after a while, leaving you with a nice steady anti-depressant effect. Little secret about effexor - some percentage of people who take the stuff end up getting the best orgasms of their life. Sorry to TMI you, but its true. I was one of them. This was 10 years ago, I still talk about it with reverence. Heads up with effexor, it can be very difficult to wean yourself off of it, so if you decide to try it, make sure you are very careful with yourself if you decide to stop the trial. Withdrawal from effexor can make you super cranky.
I have no idea what methergine is.
I ended up doing an herbal regimine for my migraine. Pills suck, IMHO. I'm trying an occipital nerve block tomorrow. Very excited.
Many chronic pain patients experience moments of believing their life isn't worth living. Its hard living with all this pain. I suggest a bit of reality check when this happens with you. There is always someone worse off than you and someone better off than you. Next time you see your neurologist, take a look at the other people in the waiting room. There are things that can happen to the human body that make migraines look like a booboo pinky finger. No matter what, you are not the saddest case ever. And you really haven't done it all yet. Not even close.