Bottoming has started to hurt

[MisterLove]

Do you have any problem or pain defecating or is it just during sex? It could be some lesion or fissure.

[Rareboy]

Get checked to make sure you don't have a fissure or something.

I'd finger the lube.....as the likely culprit.

Use something like Astroglide or Crisco.

[princealbertofb]

It also depends on what actually hurts when you're bottoming, is it the entrance or does the hurt come from inside? Maybe it's something to do with positions that aren't comfortable? Maybe now that you are a little more experienced you are engaging in it too early without sufficient preparation or loosening, and maybe the positions are unadapted to the depth of penetration. If the hurt is like soreness or inflamation, then you need to address that. It might just be due to rubbing that's become too harsh. But do see a doctor about this.
Bowyn was suggesting an STD, but if you've both been wearing condoms doing it, it would seem less likely, not totally impossible, but less likely. However, in truth, some STDs can be passed on from other sources than a penis. A mouth, a tongue ... so maybe one of you doesn't know he was carrying an STD before dating. Both need to be checked if you are carrying something. A course of antibiotics should put this right. Don't just think it'll go away, though, so do get medical advice.

[MisterLove]

Some guys take poppers and it really helps penetration but it's not the most sensible option, of course.

[Titan924]

Wow thank you all so much for the replies, we did start off using the regular K-Y and switched to the more expensive K-Y ultragel, thinking more expensive meant better. It worked great the first few times but it was almost directly after we used it that we both experienced pain. Mine was more of a "I have to go to the bathroom" type of pain once he's already inside. Entering has never really hurt because he is always very gentle and slow going in. He also thinks he may have a cut inside his rectum, but hasn't had it checked by a doctor. I also went the past week to get tested for HIV and came up negative, so the only possibility disease wise would be the STI's, which will take a week or two for the results to come back. Condom brand has remained consistent and we always do foreplay before sex to loosen up. Hope this helps!

[MisterLove]

[...] He also thinks he may have a cut inside his rectum, but hasn't had it checked by a doctor. I also went the past week to get tested for HIV and came up negative, so the only possibility disease wise would be the STI's, [...]

I'm not sure what you mean but this could be a fissure and fissures are not an STI - e.g. you could get one from a bad case of diarrhea.

[Titan924]

Sorry that was poor wording on my part! Those two things are exclusive. He thinks he may have a cut inside his rectum but that is not the reason that I got tested. I wanted to be doubly sure that I was clean since we are very much in for the long run!

[Rareboy]

....just sayin'.....oh....and get rubber sheets for even more fun.

[princealbertofb]

....just sayin'.....oh....and get rubber sheets for even more fun.

But as this is shortening, it's fatty material and so can't be used with condoms...
You need water based lubricant to use with condoms...

[Camfer]

Oil based lube can be used with non-latex condoms. It cannot be used with latex condoms.