Landlords, builders, everyone letting themselfs into my apartment on a weekly basis!! Law regarding this?

You mentioned "The Housing Act 1988" in your other question which is one of the leading statutes governing property law in England/Wales so I assume that is where you are.... each country ( even in the UK) have their own laws..........
For "landlord" read "agent" as agents are just paid by the landlord to "be them" and 24hours notice in written ( email/text etc) to inform you that there is an inspection or a repair which requires doing etc...... if like you say they are entering "usually twice a week" then they are seriously breaching the tenancy contract to the point of harassment completely illegal...... "quiet enjoyment" to live in the property is a tenants right. ...and it really doesn't matter what they wrote in your tenancy contract you signed and by law have a copy of it is statutory law meaning can not be taken away by a contract 24 hours notice IN WRITING to inform you they are entering ( doesn't need your permission ) so for inspections once every 6 months , gas check and cert annually( by law) ONLY in an emergency like fire/water leak/electric shut off can they enter without notice

So you need to write a letter keep a copy and record deliver it to the "agent" setting out they are in serious breach of contract read first so you know http://www.movebubble.com/2014/07/tenants-rights-breached-uk/ and no change speak to the housing officer at the local council who will stop the agents doing this

they cannot do this without a notice posted 24 hours in advance. the only reason someone can enter your apartment without notice is a mananger, maintanance or police if there is some kind of emergency. tell them to stop or your contacting fair housing.

Please dont answer this, didnt add info box and wont let me delete on mobile