What to do if i can't sleep at night. is it insomnia?

Yes: How good is your sleep hygiene? 1. Keep a regular bedtime & wakening time (to include weekends). Get up the same time each day, regardless of what time you fell asleep. 2. Make a regular, relaxing bedtime routine. Relaxing rituals prior to bedtime may include a warm bath or shower, aroma therapy, reading, or listening to gentle music. 3. Sleep in a dark, quiet, cool room on comfortable mattress.

Can't sleep: Talk to your doctor about this & see if you need assessed for secondary insomnia (insomnia due to other organic or psychological factors) which can be treated. Meanwhile you can try the sleep hygeine techniques. Refer to my previous responses for details about sleep hygiene.