It sounds like you might be describing existential angst or existential dread by a lack of meaning or purpose. If it's not a medical condition and you're trying to find fulfillment I would suggest a healthy dose of philosophy books (Socrates' The Republic is a good starting point, from there follow your curiosity) followed by a couple courses of psilocybin mushrooms if you're dealing with death anxiety and at least in your 20's and not prone to psychosis.

Another practical suggestion would be to instead of picking easily obtainable goals carry multiple goals; one for short term stuff that are easily completed, and a long term goal that may not even be possible to achieve. You don't get the satisfaction of accomplishing the long term goal, but it's always available for something to strive towards. Traditionally I think these would be things like honing a skill or hobby or trying to be a better person morally than you were before by putting your focus on the needs of others & relationships.