should i give formula milk na??

should i give formula milk na? baby ia turning 4mos this May. hirap na ako magpump ng BM enough lang for 3hrs naiiwan ko. she can drink 7-8oz for 3hrs. im taking natalac daily naman and other galactagogues. if rest day wholeday latch naman kami ni baby kaya di pa rin ako makapag-stock :( buti malapit lang bahay namin s office kaya nakakauwi ako tuwing breaktime. as much as possible sana BM sya hanggang 6mos. She's my only child na napabreastfeed ko exclusively. my 2 children were mixed since outbased qork ko