Oo, normal lang yan, mama! At 4 months lagi kang pagod kasi ang katawan mo ay gumagawa ng maraming changes at extra blood para sa baby, so it's natural na mawiwi ka sa bed even without doing much. A few of us pregnant moms actually experienced the same thing, one friend namin nag-collapse sa office dahil sobrang pagod, tapos normal pala. But since you're working pa rin at nauuwi kang ganyan, mas okay kung i-check mo na with your OB just to make sure everything's okay with you and baby, lalo na kung di mo pa na-monitor ng maigi ang pregnancy mo.