I think you might have a couple problems.
The oil light coming on is often caused by the seals in the oil pan leaking internally - you wont see oil leaking. This causes low oil pressure and is fairly common on these Volvo engines.
The hard starting when the engine is warmed up may be due to a leaking fuel injector, which is also a fairly common issue. Have a shop check the residual fuel pressure to see if it is within specifications.