Umar ibn Al-Khattab (may Allah be pleased with him) said, "Bring yourself into account before you are brought into account. Weight your actions before they are weighted." (Ya Ayya Al-Walad by Imam Ghazali)
This confirms that missed prayers must be made up and the previous proof is for missed fasts. They lead us to the understanding that obligations must be repeated.
The best time to make up fasts is winter or when the days are short. You can have breakfast and miss dinner then eat at four pm! (Please check your local times!)
If you cannot make up the prayers and fasts because of illness then pay the fidya for the fasts. If you do not have the money to pay for the missed fasts then seek forgiveness and pay when or if you have the money (Tahfat Al-Muluk). Even having the intention to make them up, when you cannot, is good.