06 KX 250F foul neutraling?

Okay here is the problem... can be 2nd or 3rd gear pin and my bike just like slips into neutral and revs up and then catches 2nd gear again and i dont know if its my fluid or what but it started happening the last time i rode some people i asked said to check the fluid and i haven't had a chance to ride again so if you could please tell me what you think it would be very helpful.... Thank you