What exactly did this government do wrong which resulted in such a sudden meltdown of Pakistan's economy? It must be something BIG. Just "not concentrating on economy" does not answer the question.
One of Pakistan's biggest problem is lack of energy. Did this government prohibited all energy producers from working or something? Was the energy situation somehow satisfactory under military rule?
Pakistan biggest and only problem is mistrust on present political government, causing flight of capital from Pakistan.
Your energy question ... Lack of electricity: It is not due to lack of available capability to produce electricity, but due to cost of producing electricity and people affording true cost. Pakistan needs around 17000 MW of electricity, can produce around 20000 MW of electricity but is producing around 10000 MW or less. So, even if Pakistan could have produced more, it does not matter.
Government prohibiting electricity producers: Government do not want rise in electricity price and are not providing enough funds to produce electricity at subsidised rate. Unfortunately, due to present government reputation, flight of capital caused rupee devaluation by 50 percent, and that means cost of producing electricity gone up by 50 percent just due to devaluation. I think present situation is that, if government wants to fulfil all energy demands (electricty and oil) what country needs, government would need to spend around Rs 500 billion a year in subsidy.
Satisfactory situation of energy level during military government: It was not that satisfactory, especially since 2007, though much better than today. Last year, Bhangra on road and other instability caused by political parties in Pakistan plus oil price rise (it went to $100 a barrel at one point in 2007) meant energy sector needed huge subsidy and government was not willing to spend that much, hence shortage in electricity production.