The headaches MAY be due to the type you are taking, the link above is the one I've been taking, it's very pure. One scoop is 2g and I take sometimes 4-5 scoops a day, so I take alot, but I don't nec. take it every day.
When I first started taking another brand of l-glutamine 4 years ago, I remember the doctor saying to build up to 2-3 g/day. Might try starting slow or changing to the jarrow brand. If you order from iherb and use my code of VIR110, you'll receive $5 off your first order.