I posted about exactly the same problem with my daughter about 3 weeks ago.
Since she had been born I've breastfed her but we'd always given her one bottle of expressed milk a day (usually at bedtime so DH could do it) but when she started to sleep through we stopped for a while because I started to put her down and there was no need for the bottle. After about 3 weeks we wanted to go out for a meal and leave her with nan for a couple of hours so I tried her with a bottle and she screamed the house down. She was just 3 months old at the time too so about the same age as your LO.
I read on the internet that it's quite common at around 12 weeks or so for this to happen (especially if you stop giving the bottle for a few days) because the baby starts to develop a sense of preference and decideds that it prefers to be close to mummy and have breast. It less usual if you continue with feeds.
The only advice was to perservere!!! With Poppy I sat her in her rocker chair and had a good talk to her and told her that mummy was bigger than she is so therefore she hasn't got a chance of winning the battle of wills........and that's what it was! I did it in the daytime so that I wasn't tired and wanting to get to bed and I went in with the determination that she was NOT having booby!! there was a bottle of breastmilk there so if she was hungry she could have it. It took about an hour and a half of crying and stopping and starting but she did eventually take the bottle and again and I now give her one at least every other day. I ended up having to sqirt some of the milk into her mouth when the teat was in there so that she had to close her mouth to swallow it and that when she started to suck again. Sometimes even now she'll play with it a bit before she takes it but she doesn't scream at the sight of it anymore and I don't mind if I have to leave her for a few hours now either.
She still won't take it if I'm holding her and I have to give it to her while she's sitting in her chair but I can handle that.
Some of the tips I found were
1, try to distract them while you give the bottle. e.g. put the TV on
2, have them facing away from you when you give feed so that they can't see your face
3, get someone else to do it for you and you leave the house completely
4, don't hold them while you give the bottle (give the feed while baby is in a chair etc)
5, try the bottle in the day when baby isn't too tired
6, be patient. Don't expect baby to take a bottle straight away if you haven't given one in a couple of weeks.
7, just try to get baby to take a couple of ounces first off and gradually increase.
I can't remember anymore off the top of my head but there are quite a few on other websites if you do some research.
good luck..... I hope it works for you