Nigeria was in a recession and exited a few months back per [12]. This bbc video tries to answer the question of why the recession happened [13]
The 2017 budget has N7.3 Trillion expenses with N4.94 Trillion revenue (of which oil revenue is N1.99 Trill)and a deficit of N2.3 Trillion. The oil revenue is not near enough. A good portion of their expenses looks to be capital expenditures (infrastructure and security) and debt servicing. "In 2017, debt servicing is projected to increase by 22 percent, which is above the current inflation level, indicating a real increase in the country’s debt burden as the FG plans to increase borrowings. " [0]
The deeper reasons might be the history - civil war, dictatorships, communal violence over decades including an insurgency and concomitant vicious cycle and corruption. Things look to be getting better.
Poverty is huge. [1] mentions 33% as below the poverty line ($1.90/day per [8]). India where I'm from as a comparison has 12.4% per [10]. Huge inflation - 9% in 2015 per [1] but now at 16% per [11]
[2] mentions three causes for poverty in Nigeria - income equality, ethnic conflict and political instability.
Civil war right after independence led to a dictatorship [9]. The oil boom in the 70s increased the govt's (dictatorship's) money but "did little to enhance its political and administrative capacity, but did increase incomes and the number of jobs that the governing elites could distribute to their clients". [6]
Looks like the return to democracy in 1999 (Fourth Nigerian Republic [3]) is when things started to turn for the better with civilian rule. Still with lots of violence [4] and a religious insurgency by Boko Haram at least until Dec 2015 ("technically defeated") [5]. Existing poverty is itself mentioned as as a cause for the rise of Boko Haram and they also made things much, much worse - "roughly 10,000 deaths since 2011 and roughly 2.6 million displaced Nigerians" (and more economic impact) [6]. Corruption seems to be widespread with scams listed till 2015[7].
The 2018 proposed budget tries to reduce the deficit and forecasts a 40% growth of the non-oil revenue (though many of the expenditure items have a similar growth). [14]
[0] https://home.kpmg.com/ng/en/home/insights/2017/06/2017-budge...
[1] https://en.wikipedia.org/wiki/Economy_of_Nigeria
[2] https://en.wikipedia.org/wiki/Poverty_in_Nigeria
[3] https://en.wikipedia.org/wiki/Fourth_Nigerian_Republic
[4] https://en.wikipedia.org/wiki/List_of_massacres_in_Nigeria
[5] https://en.wikipedia.org/wiki/Boko_Haram
[6] https://en.wikipedia.org/wiki/Economic_history_of_Nigeria#Bo...
[7] https://en.wikipedia.org/wiki/Corruption_in_Nigeria
[8] https://en.wikipedia.org/wiki/Poverty_threshold
[9] https://en.wikipedia.org/wiki/History_of_Nigeria#First_perio...
[10] https://en.wikipedia.org/wiki/Poverty_in_India
[11] https://tradingeconomics.com/nigeria/inflation-cpi
[12] https://www.reuters.com/article/us-nigeria-gdp/nigerias-econ...
[13] http://www.bbc.com/news/av/world-africa-37230696/nigeria-in-...
[14] https://www.pwc.com/ng/en/assets/pdf/pwc-2018-nigerias-budge...