Why do I always forget to put words in sentences when I write?

For example, when wanting to write the sentence "I love you very much.", I'll sometimes write "I you very much" This happens a lot when texting various sentences or writing on computers in general. Does this happen to you. I end up sounding like a caveman when I write sometimes. Like "I am going to the store." coming out as "I going to the store." Its annoying the crap out of me.