For physical pain, you can use both 疼 and 痛. The young generation uses 痛 more often. For 痛, it can also be used for Psychological pain, like 心痛, 痛苦... For 疼, it can be used as a verb, means "dote".

in ancient chinese,many words is same meaning,with the chiese devolping,like 疼and 痛,they have same mean,sometimes u can use it in the same time,sometimes u cannt

痛 and 疼 have the same meaning sometimes,especially describe physical pain. but with other letter have another meaning. e.g 痛=hurt, sorrow. like words 痛苦, presentation states 疼=pain,ache.its noun. the psychological pain. 心疼 describe the older people loves their children ,grandchildren. dote,like words 疼爱