How can I stop constantly losing things?

Put them in one spot. Try to put them in areas at home where you will always remember that are visible where you can't miss it. For example, i always put my keys in the same place every time. So i never lose them. Either in my purse or on the counter near the door so they are ready for me. There is also a product called 'tile' that you can attach to things so you can find them with iphone.
Focus, focus, focus. If you make a conscious effort to stay more grounded, centered, focused, and "in the moment, " then you may be able to get a little more on top of your game. It sounds as if things get you distracted and your mind wanders from the task at hand. Trying to stay more "present" can really make a difference. Meditating might also prove useful for you.