I would like to make my own shouts

See this question for guidelines.

Secondly Why there isn't  a translation for every word  (Thu'um) ?

The dragon language was made by Bethesda for a single game, Skyrim. They only created the words they needed to write the shouts, dragon names, Word Walls, songs and dialogue because to do otherwise would have been a waste of developer time. Unfortunately this means there are gaps in the vocabulary.

The dictionary should be completely comprehensive, but if there are any dragon words missing from the game, let us know and we can add them.

The official language contains 649 words that are found in (or sometimes out) of Skyrim, usually in Shouts, word walls, or dialogue. There is only a limited amount of dragon language material, so a lot of English vocabulary doesn't have a direct dragon equivalent. Some words can come close, though. For "regenerate," you could use vokrii 'to restore (lit. un-kill)'. "Source" could be expressed metaphorically with bormah 'father' or monah 'mother' (e.g. "Necessity is the mother of invention").

If you can't find a translation, consider searching the Legacy Dictionary, which contains over 5,000 fanmade words. Just note that these words aren't part of the official language.