Doindinho is a charming and somewhat informal diminutive of doído, which means 'sore' or 'hurting'. Adding the suffix -inho softens it, making it 'a little sore' or 'a little hurting'.
In the context of this song, Djavan uses doindinho to express being driven 'a little crazy' or 'lovesick' by the woman he's singing about. It perfectly captures the playful yet intense emotional state of being deeply smitten and slightly tormented by love, making it a unique and memorable word.
Djavan's "Não É Um Bolero" is a really fun, almost exasperated look at a confusing love. Our singer is completely smitten, calling his love "bela e fera" [beautiful and a beast], but she's also incredibly unpredictable. He feels like she doesn't "pondera" [consider] his feelings, leaving him "doindinho" [a little crazy] and feeling like he crumbles "sozinho" [alone] when she shrugs him off.
He's asking, if there's so much more between them, why live through "dias sombrios" [gloomy days]? For him, this isn't some dramatic bolero; it's "amor sincero, que a tudo resiste" [sincere love that resists everything]. He makes it clear that not having her by his side leaves him "abalado" [shaken] and that "nada é mais triste" [nothing is sadder]. He even says he has everything, but "me falta tudo se eu não tenho você" [I lack everything if I don't have you]. It's a sweet, slightly desperate plea for clarity and commitment from a love that's clearly got him wrapped around her finger!