My girl had similar after every feed for about a week when she caught a viral thing, so three days is still early lah. Since she's got the runny nose and cough too, it's likely all connected, but I'd bring her to see the PD just to be safe especially since she's an infant, just to rule out anything that needs attention. Keep her well hydrated in the meantime and watch her nappy output and energy levels. Hope she feels better soon.