PLEASE HELP

He whines all the time. If he cant see my other dog, he whines. If he cant see me, he whines. If he thinks he is alone in the house, he HOWLS. It has become so bad that I received a complaint from my condo place about my dogs being left alone in the house and constant barking/howling taking place. I knew he may have howled once or twice when we first leave but I never knew that apparently he is constantly doing it. He isnt left alone often and he is always in here with my other dog, so I dont know what it is. Yesterday he peed in the house, so I made him sit in the family room with us for a few minutes instead of having free roam of the house. He whined and everyone including the other dog was in there. I dont know what this is because of or how I can fix it. He has been around the other dog since the day we got him, but the severe whining and howling has just started. Is there anything I can do to help him?