aspartame/equal/blue packet is the most common sweetener in diet soda/drinks and it causes headaches in many.

It definitely causes them for me. I gave up all sweeteners/sugar for a month last April as a personal challenge. I was shocked that I didn't get a headache at all that whole time. The first time I had a diet soda afterward I got a wicked headache. It took me 2 or 3 times more and I decided no more diet soda for me ever. Once I made the connection it was easy to choose another drink.

That month-long challenge was really productive for me, I think. Even though I did reintroduce some sweetener in small amounts I'm much more conscious of my use, pickier about which sweeteners I choose, and overall reduced my intake by about 70%.