C150 pilot flying reported a loss of oil pressure and erratic engine RPMs after leveling off in cruise. The reporter safely diverted to a nearby airport.

Narrative

While departing from ZZZ; all engine indications were in the green and consistent during cruise climb to 5;500 ft. MSL for the cruise altitude. The oil pressure gauge was reading just below the white 'optimal' mark; but held a consistent indication in the green. Within a few minutes of leveling off at 5;500 ft.; engine RPMs went from 2;600 to about 1;900. Immediately enriched the mixture; but RPMs continued to drop. Engine RPMs fluctuated back up to low 2;000s; before dropping down closer to 1;500 RPM. Fluctuations persisted with consistent throttle setting. Carburetor heat did not help. The oil pressure decreased below its steady figure on the electronic display of 28 - 29 points; the lowest noted was 14 points during descent. Oil temperature did not increase. Started to return back towards ZZZ1 within a minute of engine issues beginning; and within a minute [requested priority handling] over the ZZZ TRACON frequency; announced intentions to divert to ZZZ1; and mentioned the engine issues. Was handed off to ZZZ1 Tower; cleared to land on Runway XX; but due to being on a high approach; switched to Runway XY in order to have the longer runway. Landed; taxied to ramp. While taxiing; oil pressure rose back up; but not as high as it was in flight. After shutting off plane; confirmed that the oil cap/dipstick was still secured; and the level of oil was similar to what was indicated during preflight inspection. Unsure of the exact issue; but I believe it could be due to some obstruction in the oil system or issue with the oil pump. The FBO which owns the plane will be investigating.Regarding human performance; overall I do not believe there were any particular misguided perceptions; judgements; or decisions that were made in an erroneous manner that caused safety of flight issues. My actions to divert to ZZZ1 were made timely; and well executed. If anything; I should not have trusted the slightly sub-optimal oil pressure indication despite it being in the green and consistent.