Can -NH2 groups get nitrated? In the chapter of amines, and I see reaction occuring between amines and nitrous acid. However I am thinking why I don't see reactions of amines also react $\ce{HNO3}$ in presence of stronger acid like $\ce{H2SO4}$, that can protonate $\ce{HNO3}$, causes $\ce{H2O}$ to leave and then finally have amines to react with $\ce{NO2}$, making nitroamines?
Yes, you can form a nitroamine (nitramine) from a secondary amine and nitric/sulfuric acids. Some explosives have a nitramine structure (e.g. tetryl, RDX, HMX, HNIW).