Hard to shift, sometimes it will not go into gear

Hi, I have a 1996 Mazda B2300 with a 2.3 L motor and a 5 speed manual transmission (closed system) with 195,000 miles. I have had this vehicle since it was new and have done all of work on it myself. I replaced the clutch about 1 year ago. Lately, within the past couple of months, it has become very hard to shift at times. No rhyme or reason. No particular RPM, no particular gear. And not always. Sometimes it is warm out, sometimes cold. Sometimes the vehicle is warmed up, sometimes not. Sometimes I drive a couple of hundred miles with no issue and then all of a sudden, it won't go into gear. This is most noticeable when trying to get into 1st or 2nd gears. When I changed the clutch, I drained the transmission due to my doing the job alone and making it easier.