Poor sweetheart sick after eating eggs and biscuits (7)
I believe the answer is:
cookies
'biscuits' is the definition.
('cookie' can be a synonym of 'biscuit')
'poor sweetheart sick after eating eggs' is the wordplay.
'poor' indicates anagramming the letters.
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'after eating' indicates putting letters inside.
'eggs' becomes 'oo' (visually resembles two eggs).
'e'+'sick'='esick'
'esick' is an anagram of 'ckies'.
'ckies' enclosing 'oo' is 'COOKIES'.
'and' is the link.
(Another definition for cookies that I've seen is " American biscuits".)