I agree - you should list your specs.
However, there is no point in having an AV software that makes you suffer using your pc - and AV software CAN make your pc slower, no doubt about it.
What you have to do is as follows:
1. check in the task manager if there are programs that overload the cpu/disk/memory. If there are, try to shut them and then check again if your pc run slow.
2. In case the above doesn't help and you suspect this is your AV , uninstall it and see if your pc is back in business.
3. If (2) did help, then there might some other problem or you've just didn't uninstalled your AV fully.
4. If it does, you have two options:
a. you don't really need an AV SW because you don't do dangerous staff (opens unknown exe and such) + you are using modern updated OS (Windows 7, XP SP3, Ubuntu + updates and so on).
=> you can just use the firewall + maybe some basic AV software, like Avast.
b. You are concerned about your pc safety. Then you can try other AV softwares, like NOD32 or AVG and see which is more suitable for you.
I myself don't use AV at all. Only Win7 64 + updates + firewall. About a year now and it's all good.