Fatigue in the Second Trimester Please help

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I am 16 weeks and 6 days almost on my 17th week of being pregnant and i am struggling to stay awake even at work i have lost all means of being motivated to work im tiered all the time that it makes me seriously depressed my job is basically recruiting engineers for overseas projects so to make it worse i have to stare at a PC Screen the whole day! during the day i find myself going to the loo and falling asleep for what i only fell asleep for a second literally felt like i was sleeping for 10 hours i find myself falling asleep everywere, this is my third pregnancy and this is the first time i have experienced this, PLEASE help what can i do to not be this tiered any more?