Hello I'm doing a basement finish. I had to jackhammer the concrete subfloor tap into the main line and route a toilet and shower drain. I messed up on my initial plumbing and put a ptrap under my toilet drain. I had to cut the fitting off and put a ninty going straight up from my santee attached to my main line in order to bring the toilet up anywhere near where i needed to be. The water flow comes down the mainline 90s under the concrete foundation and drains to the left across the basement. Now when a heavy laundry load is ran with toilets being flushed i am having soap and water backup out my toilet drain. Now i tapped into the main line very close together and essentially budded my santi's straight to one another one leading out to the shower one to the toilet I put fall on both of my santi's as I installed them and assured proper fall on all my piping. I don't know if I created a trap by putting the santy's too close together I also and wondering if I need to extend the line out for my toilet further away from that main line drain if that will fix my issue. I never take good pictures but I took pictures initially when I piped everything when I had the P-trap installed underneath the toilet i since cut the P-trap fitting itself off and fit a 90 fitting on there directly going up to the toilet so the toilet drain is very close to the mainline I'll attach photos and would appreciate any advice. All 3inch piping on mainline.