13 weeks. Could be that he is a little under the weather or even beginning to teeth?
Have you tried getting in the bath with him? DS only had one bath rejection period (about 12 months) and we solved it by me getting in with him a few times (after which he felt secure and happy again ).
I would try to continue with it, but keep it brief and be very physically and vocally reassuring (lots of bright, breezy conversation and cuddles before and after, maybe a little light baby massage). Those who get out of the habit often find it harder to get back into it.
If you do it at bedtime, could it be that he is too tired or hungry to enjoy it? Maybe bring it forward half an hour and see if that helps, or do it just after his afternoon feed then playtime til his bedtime feed?
My ds is 13 weeks and up until a couple of weeks ago he absolutely loved bath time, smiling and cooing when he was in the water and hated it when we took him out. Now it's the other way around!! He hates being in the bath and screams the place down, and doesn't stop until you take him out! I haven't done anything different, the water is warm enough, as is the room. Has anyone else experienced this sudden change? and will he eventually learn to like baths again?? TIA xx