cant burp newborn

i find it difficult to burp my baby after feeds, and its just me because everyone else can do it no problem. I sit her in different positions and still get nothing, sometimes i go like 10mins trying to burp her and i get nothing. Sometimes she does burp for me, but only on the odd occasion. As soon as i ask someone to take over, she burps straight away! But im not always with someone else so sometimes i just have to leave her without being burped. It doesnt cause her pain, she doesnt cry like she is gassy, she just goes to sleep like normal, but i just wish i could do it.. any tips? she is 3 weeks old, formula fed and does have infacol before each feed.