Once 30 minutes is up, taste the broth. It shouldn't have any saltiness to it but it should have some lemongrass or lime leaves flavor. If it doesn't, cook it for another 15 minutes.
Once you have finished cooking the broth, remove all the spices and aromatics. They are not meant to be eaten, only to flavor the soup.
Turn the heat back up to medium
Add in the chili paste and stir it until it dissolves.
Once the chili paste has dissolved, put in the vegetables and mushrooms and cook them for 1 minute.
Add in the shrimp and cook it for 1 minute. (Careful not to overcook it. Shrimp cooks very quickly, as long as it is fully thawed.)
Turn off the heat
Add in the fish sauce, lime juice, and sugar. Stir and taste. Adjust it to your liking. (Add more lime juice if you like it more sour etc)
Place the glass noodles in a serving bowl and ladle the piping hot soup into the bowl to cover the noodles. The heat will cook it. Let it soak up the soup for a few minutes.