Do you find it difficult to engage 1st also when stationary, does it grind when you try to select reverse?
During the cold weather its not uncommon to have difficulty engaging gears on a lot on manual gearboxes, usually 1st, then 1st to 2nd, just due to the gearbox oil being cold.
If it does grind on reverse and doesn't want 1st either the clutch could well be dragging (not fully disengaging), best to get that sorted asap as it will put unnecessary stress on the syncromeshes