Why this is a red flag: If sex is feeling like a chore, it's important to ask yourself why it feels that way. Does it feel that way because you feel sex is expected of you or that you expect it of your partner? Does it feel like something you think you should be doing?
When something begins to feel like a chore, it's probably because we've mentally made it into one. I know—probably not what you wanted to hear, but alas, it's generally the truth.
Sex, because of how our society portrays it, is made to seem like this extremely sexy event (which it absolutely can be) that happens naturally (which it can) every single time, and each person involved is pleasured to their desired need (which can happen). However, what society and media don't tell you is this: There's a lot of communication, intentionality, planning, and messiness involved in sex—like, a lot.
So, if sex is feeling like a chore, try saying something like this to your partner: "Hey, sex is feeling like a bit of a chore to me lately, and that makes me sad because I really love connecting with you in this way. Could we talk about some possible ways to meet both of our needs?"