If it gets bitter and tough when it gets old, perhaps you
should only eat it when it's young. Especially if you have food sensitivities and a proclivity to enjoying foods that are too bitter for most other people (as on your
thread about mugwort), you might want to stick to eating the young plant.
There are many resources available
online and in
books about edible wild plants. For example, www.eattheweeds.com by Green Deane, and lots of books. Read up on the plants and at first try following the suggested time of collection (spring shoots, mature plant, whatever) and suggested method of use (salad, cooking green,
medicinal tea, whatever). Once you've tried it a few times and you don't have a negative reaction, and if you like it a lot, then maybe try eating more of it. But the fact that you chowed down on mugwort as a salad three meals in a row suggests to me that you don't have the aversion to bitter plants that most people do, so you should read up and use caution. Especially since you have other food allergies already.