The Bible has a lot to say on sexual immorality, how Christians should be living their lives and despite what some may claim, God does care very much what we do with our bodies. Here are just some of the many verses on this subject:
'Let marriage be held in honour among all, and let the marriage bed be undefiled, for God will judge the sexually immoral and adulterous.'
(Hebrews 13:4)
'But among you there must not be even a hint of sexual immorality, or of any kind of impurity, or of greed, because these are improper for God’s holy people. Nor should there be obscenity, foolish talk or coarse joking, which are out of place, but rather thanksgiving. For of this you can be sure: No immoral, impure or greedy person - such a person is an idolater - has any inheritance in the kingdom of Christ and of God. Let no one deceive you with empty words, for because of such things God’s wrath comes on those who are disobedient. Therefore do not be partners with them.' (Ephesians 5:3-7)
“I have the right to do anything,” you say - but not everything is beneficial. “I have the right to do anything” - but I will not be mastered by anything. You say, “Food for the stomach and the stomach for food, and God will destroy them both.” The body, however, is not meant for sexual immorality but for the Lord, and the Lord for the body. By his power God raised the Lord from the dead, and he will raise us also. Do you not know that your bodies are members of Christ himself? Shall I then take the members of Christ and unite them with a prostitute? Never! Do you not know that he who unites himself with a prostitute is one with her in body? For it is said, “The two will become one flesh.” But whoever is united with the Lord is one with him in spirit.
Flee from sexual immorality. All other sins a person commits are outside the body, but whoever sins sexually, sins against their own body. Do you not know that your bodies are temples of the Holy Spirit, who is in you, whom you have received from God? You are not your own; you were bought at a price. Therefore honour God with your bodies. (1 Corinthians 6:12-20)
'Now for the matters you wrote about: “It is good for a man not to have sexual relations with a woman.” But since sexual immorality is occurring, each man should have sexual relations with his own wife, and each woman with her own husband. The husband should fulfil his marital duty to his wife, and likewise the wife to her husband. The wife does not have authority over her own body but yields it to her husband. In the same way, the husband does not have authority over his own body but yields it to his wife. Do not deprive each other except perhaps by mutual consent and for a time, so that you may devote yourselves to prayer. Then come together again so that Satan will not tempt you because of your lack of self-control. I say this as a concession, not as a command.'
(1 Corinthians 7:1-7)
'For all that is in the world - the desires of the flesh and the desires of the eyes and pride of life - is not from the Father but is from the world.' (1 John 2:16)
'It is God’s will that you should be sanctified: that you should avoid sexual immorality; that each of you should learn to control your own body in a way that is holy and honourable, not in passionate lust like the pagans, who do not know God; and that in this matter no one should wrong or take advantage of a brother or sister. The Lord will punish all those who commit such sins, as we told you and warned you before. For God did not call us to be impure, but to live a holy life. Therefore, anyone who rejects this instruction does not reject a human being but God, the very God who gives you his Holy Spirit.'
(1 Thessalonians 4:3-8)
It’s clear from reading the Song of Songs that God intends sex between a husband and wife to be loving, mutually enjoyable, pleasurable and not exclusively for reproduction.
There are a few things that married couples should not partake in. These include the involvement of a third party, such as threesomes, adultery and the use of pornography.
I would also be uncomfortable with having sex during a period, but that is not so black and white. I think your concerns about anal sex are justified. Use your God given discernment and also pray about this. If it’s pricking your conscience there’s probably a good reason for this.