L.L.
It could be teething or even at this age nightmares can begin. My daughter sometime wakes up several times during the night and crying a bit and after 5 minutes, she goes back to sleep.
Does she sleep a long time during her naps in the day? This could cause her to have shorter sleep time at night. If so, try waking her from her nap 15 minutes earlier. Let her be more active during the day so she is exhuasted by the time bed time comes around.