fuel system help

[E36&8]

car= 95" 325is
as i'm driving and holding constant speed at 100/kmh the L/100 km needle would start moving right & left really quick and the engine would start to struggle, there is also a loss of power

any ideas as it only started doing after i was running low on gas but i gassed up right away and ever since i been trying to find the problem.

no check engine lights or anything like that