Baby keeps latching on and off

We are 3 weeks now. Trying to establish breastfeeding. The past 3 days have been awesome with little one latching on sucking and drinking. She is fussy at certain times but feeding time has been much better than before.

However the last few feeds she has constantly been coming off and latching back onto me. She gets really frustrated and does this multiple times. Eventually I had to try and settle her end give her a top up for formula.

I don't understand why she is suddenly coming on and off. I do think I have a slow let down and therefore do compressions during feeds.

I have had a minor cold for the past 2 days - that wouldn't affect my supply or let down would it?

I don't know what to do as I thought we were making some progress! Q