I had similar problems with against 3 attacker opposition...
You have couple of diferent setups you have to dinstict and to recognize...
First thing, you need to see in formation screen how those tree setup... Which one is lower position the other, then you can get some clues about how those three function. Also, you need to see position of oppositon fullbacks and opposition midfield three...
1. variant
Their setup looks like this:
FC FC
FC
_______________________(midfield line)
MC MC MC
FB FB
C D CD
This one is direct style of game, in which oppositon three midfielders are holding, and middle forward is one conecting midfield and attack, while Fb are giving width in second wave and usually they cros low to two fast strikers behind your defence.
For this opponent setup your attacking formation will hit wall and your setup with two bombing FB will leave you exposed to trough passes. Best way to defend this setup is basecly to control pace of game. You need much more methodical game, more controled wiht very aggresive closing down to FB and midfield trio, and You might want to man mark with one midfielder this central forward, to distrupt opponents gameplan. When your stopers are defending one on one his fast strikers against direct ball from deep, it will be much easier for you. But main thing is to force his stopers to send the balls forward, not midfielders and not FB-s, hence, you tell your team not to close down them ever.
In attacking faze, force wings, as this is main weaknes of this formation.
2. variant
Second setup is similar, but more narrow one:
FC FC
FC
CM
__________________________
CM CM
FB CD CD FB
This one has tall player in middle and probably two advance forwards. It is still direct passing, but it is not two layerd attack as previous one. Ball goes to his FC central which flics on to cm or two other fC-s, which are runing wide with ball and then crossing floating cross to central attacker. His fulbacs are much more reserved and if they do come forward, they will cross from deep, not byline.
This style of play is simplyer, but you do need tall and powerfull defender to chelinge his gamplan. If you dont, You will certnaly have problem here. You may also want to put your fullbacsk to more defesive role (support instead of attacking duty) and to tell them to sit narrower in order to close gaps in defence that his advanced forwards try to exploite.
Regarding attacking part, this one is hard to break, as this one does not leave holes behind defence. You need to use faster movment to get them unguarded and to unsettle their defence, so higher tempo, early crosses, more direct play also... It will also leave you less exposed if your first ball forward does not pass to your player. Here Treq role or even TM - att role for your striker would be good idea, and depending on him you need to choose low or float crosses (if he is fast, then low, if he is tall then float). This way you will create space for your AP, and will be able to unsetlle his defence and create some space.
3. variant
FC
FC FC
CM
__________________
CM CM
FB FB
CB CB
This is possesion type of game. Two side FCs together with CM-s and FB are creating triangles and they try to move the ball until they create space to run into...
It is more vunarable at back, but it may be dificult for you to defend as well. I solved it by overloading his fullbacks and by marking his advanced CM. There is also option to man-mark his midfied three and fb and force him to send long balls forward, as chances are their forwards are les effective in aire then your CB-s. But be aware, if his players have high workrate and good movement of the ball, and your marking players have low work rate, concetration or marking, you may be making more damage to yourself then good...
Also, it may be use to you, as these formations exploite space that you leave behind, if you deny them this space, you may solve your problems. If you try to close down his CB-s with your FC and AMC (shout close down more to two of them), this will give your other players time to pull back to defensive positions, and with team shout close down less, you will have good, solid defensive shape. But this will tire your two advanced players more, so you will probably need reservs for them...