The phrase "achingly sweet" is often used to describe something that is overwhelmingly sweet or sentimental. Synonyms for this phrase might include cloying, sugary, saccharine, syrupy, or sentimental. Alternatively, you could use terms like overly sweet, overly sentimental, sickeningly sweet, heavily saccharine, or excessively sugary. These terms all convey the same idea of something that is too sweet or sentimental to be enjoyable. Whether you're describing food, a person's personality, or a situation, using these synonyms can help to add nuance and depth to your language and make your writing more expressive.