One thing that I find exasperating about German is the number of ways to form plurals.
Even though there seem to be no rules, I will show you it is not as bad as it seems. Let's take a look at them.
1. International words (from English, French, Latin,...)
2. Words with the ending -en und -er
3. Feminine words
4. Words with the root vowels -a- /-o- /-u- need an Umlaut
5. Approximately 80% of masculine and neuter words
...do you really expect me to feel better now?
Well, I didn't invent the German language. You'll get used to it... plurals will start to sound right or wrong at some point. Have faith!